/*
 * Copyright © 2014 Red Hat
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting documentation, and
 * that the name of the copyright holders not be used in advertising or
 * publicity pertaining to distribution of the software without specific,
 * written prior permission.  The copyright holders make no representations
 * about the suitability of this software for any purpose.  It is provided "as
 * is" without express or implied warranty.
 *
 * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
 * OF THIS SOFTWARE.
 */

#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/seq_file.h>

#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
#include <linux/stacktrace.h>
#include <linux/sort.h>
#include <linux/timekeeping.h>
#include <linux/math64.h>
#endif

#include <drm/drm_atomic.h>
#include <drm/drm_atomic_helper.h>
#include <drm/drm_dp_mst_helper.h>
#include <drm/drm_drv.h>
#include <drm/drm_print.h>
#include <drm/drm_probe_helper.h>

#include "drm_crtc_helper_internal.h"
#include "drm_dp_mst_topology_internal.h"

/**
 * DOC: dp mst helper
 *
 * These functions contain parts of the DisplayPort 1.2a MultiStream Transport
 * protocol. The helpers contain a topology manager and bandwidth manager.
 * The helpers encapsulate the sending and received of sideband msgs.
 */
struct drm_dp_pending_up_req {
        struct drm_dp_sideband_msg_hdr hdr;
        struct drm_dp_sideband_msg_req_body msg;
        struct list_head next;
};

static bool dump_dp_payload_table(struct drm_dp_mst_topology_mgr *mgr,
                                  char *buf);

static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port);

static int drm_dp_dpcd_write_payload(struct drm_dp_mst_topology_mgr *mgr,
                                     int id,
                                     struct drm_dp_payload *payload);

static int drm_dp_send_dpcd_read(struct drm_dp_mst_topology_mgr *mgr,
                                 struct drm_dp_mst_port *port,
                                 int offset, int size, u8 *bytes);
static int drm_dp_send_dpcd_write(struct drm_dp_mst_topology_mgr *mgr,
                                  struct drm_dp_mst_port *port,
                                  int offset, int size, u8 *bytes);

static int drm_dp_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
                                    struct drm_dp_mst_branch *mstb);
static int drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
                                           struct drm_dp_mst_branch *mstb,
                                           struct drm_dp_mst_port *port);
static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
                                 u8 *guid);

static int drm_dp_mst_register_i2c_bus(struct drm_dp_aux *aux);
static void drm_dp_mst_unregister_i2c_bus(struct drm_dp_aux *aux);
static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr);

#define DBG_PREFIX "[dp_mst]"

#define DP_STR(x) [DP_ ## x] = #x

static const char *drm_dp_mst_req_type_str(u8 req_type)
{
        static const char * const req_type_str[] = {
                DP_STR(GET_MSG_TRANSACTION_VERSION),
                DP_STR(LINK_ADDRESS),
                DP_STR(CONNECTION_STATUS_NOTIFY),
                DP_STR(ENUM_PATH_RESOURCES),
                DP_STR(ALLOCATE_PAYLOAD),
                DP_STR(QUERY_PAYLOAD),
                DP_STR(RESOURCE_STATUS_NOTIFY),
                DP_STR(CLEAR_PAYLOAD_ID_TABLE),
                DP_STR(REMOTE_DPCD_READ),
                DP_STR(REMOTE_DPCD_WRITE),
                DP_STR(REMOTE_I2C_READ),
                DP_STR(REMOTE_I2C_WRITE),
                DP_STR(POWER_UP_PHY),
                DP_STR(POWER_DOWN_PHY),
                DP_STR(SINK_EVENT_NOTIFY),
                DP_STR(QUERY_STREAM_ENC_STATUS),
        };

        if (req_type >= ARRAY_SIZE(req_type_str) ||
            !req_type_str[req_type])
                return "unknown";

        return req_type_str[req_type];
}

#undef DP_STR
#define DP_STR(x) [DP_NAK_ ## x] = #x

static const char *drm_dp_mst_nak_reason_str(u8 nak_reason)
{
        static const char * const nak_reason_str[] = {
                DP_STR(WRITE_FAILURE),
                DP_STR(INVALID_READ),
                DP_STR(CRC_FAILURE),
                DP_STR(BAD_PARAM),
                DP_STR(DEFER),
                DP_STR(LINK_FAILURE),
                DP_STR(NO_RESOURCES),
                DP_STR(DPCD_FAIL),
                DP_STR(I2C_NAK),
                DP_STR(ALLOCATE_FAIL),
        };

        if (nak_reason >= ARRAY_SIZE(nak_reason_str) ||
            !nak_reason_str[nak_reason])
                return "unknown";

        return nak_reason_str[nak_reason];
}

#undef DP_STR
#define DP_STR(x) [DRM_DP_SIDEBAND_TX_ ## x] = #x

static const char *drm_dp_mst_sideband_tx_state_str(int state)
{
        static const char * const sideband_reason_str[] = {
                DP_STR(QUEUED),
                DP_STR(START_SEND),
                DP_STR(SENT),
                DP_STR(RX),
                DP_STR(TIMEOUT),
        };

        if (state >= ARRAY_SIZE(sideband_reason_str) ||
            !sideband_reason_str[state])
                return "unknown";

        return sideband_reason_str[state];
}

static int
drm_dp_mst_rad_to_str(const u8 rad[8], u8 lct, char *out, size_t len)
{
        int i;
        u8 unpacked_rad[16];

        for (i = 0; i < lct; i++) {
                if (i % 2)
                        unpacked_rad[i] = rad[i / 2] >> 4;
                else
                        unpacked_rad[i] = rad[i / 2] & BIT_MASK(4);
        }

        /* TODO: Eventually add something to printk so we can format the rad
         * like this: 1.2.3
         */
        return snprintf(out, len, "%*phC", lct, unpacked_rad);
}

/* sideband msg handling */
static u8 drm_dp_msg_header_crc4(const uint8_t *data, size_t num_nibbles)
{
        u8 bitmask = 0x80;
        u8 bitshift = 7;
        u8 array_index = 0;
        int number_of_bits = num_nibbles * 4;
        u8 remainder = 0;

        while (number_of_bits != 0) {
                number_of_bits--;
                remainder <<= 1;
                remainder |= (data[array_index] & bitmask) >> bitshift;
                bitmask >>= 1;
                bitshift--;
                if (bitmask == 0) {
                        bitmask = 0x80;
                        bitshift = 7;
                        array_index++;
                }
                if ((remainder & 0x10) == 0x10)
                        remainder ^= 0x13;
        }

        number_of_bits = 4;
        while (number_of_bits != 0) {
                number_of_bits--;
                remainder <<= 1;
                if ((remainder & 0x10) != 0)
                        remainder ^= 0x13;
        }

        return remainder;
}

static u8 drm_dp_msg_data_crc4(const uint8_t *data, u8 number_of_bytes)
{
        u8 bitmask = 0x80;
        u8 bitshift = 7;
        u8 array_index = 0;
        int number_of_bits = number_of_bytes * 8;
        u16 remainder = 0;

        while (number_of_bits != 0) {
                number_of_bits--;
                remainder <<= 1;
                remainder |= (data[array_index] & bitmask) >> bitshift;
                bitmask >>= 1;
                bitshift--;
                if (bitmask == 0) {
                        bitmask = 0x80;
                        bitshift = 7;
                        array_index++;
                }
                if ((remainder & 0x100) == 0x100)
                        remainder ^= 0xd5;
        }

        number_of_bits = 8;
        while (number_of_bits != 0) {
                number_of_bits--;
                remainder <<= 1;
                if ((remainder & 0x100) != 0)
                        remainder ^= 0xd5;
        }

        return remainder & 0xff;
}
static inline u8 drm_dp_calc_sb_hdr_size(struct drm_dp_sideband_msg_hdr *hdr)
{
        u8 size = 3;
        size += (hdr->lct / 2);
        return size;
}

static void drm_dp_encode_sideband_msg_hdr(struct drm_dp_sideband_msg_hdr *hdr,
                                           u8 *buf, int *len)
{
        int idx = 0;
        int i;
        u8 crc4;
        buf[idx++] = ((hdr->lct & 0xf) << 4) | (hdr->lcr & 0xf);
        for (i = 0; i < (hdr->lct / 2); i++)
                buf[idx++] = hdr->rad[i];
        buf[idx++] = (hdr->broadcast << 7) | (hdr->path_msg << 6) |
                (hdr->msg_len & 0x3f);
        buf[idx++] = (hdr->somt << 7) | (hdr->eomt << 6) | (hdr->seqno << 4);

        crc4 = drm_dp_msg_header_crc4(buf, (idx * 2) - 1);
        buf[idx - 1] |= (crc4 & 0xf);

        *len = idx;
}

static bool drm_dp_decode_sideband_msg_hdr(struct drm_dp_sideband_msg_hdr *hdr,
                                           u8 *buf, int buflen, u8 *hdrlen)
{
        u8 crc4;
        u8 len;
        int i;
        u8 idx;
        if (buf[0] == 0)
                return false;
        len = 3;
        len += ((buf[0] & 0xf0) >> 4) / 2;
        if (len > buflen)
                return false;
        crc4 = drm_dp_msg_header_crc4(buf, (len * 2) - 1);

        if ((crc4 & 0xf) != (buf[len - 1] & 0xf)) {
                DRM_DEBUG_KMS("crc4 mismatch 0x%x 0x%x\n", crc4, buf[len - 1]);
                return false;
        }

        hdr->lct = (buf[0] & 0xf0) >> 4;
        hdr->lcr = (buf[0] & 0xf);
        idx = 1;
        for (i = 0; i < (hdr->lct / 2); i++)
                hdr->rad[i] = buf[idx++];
        hdr->broadcast = (buf[idx] >> 7) & 0x1;
        hdr->path_msg = (buf[idx] >> 6) & 0x1;
        hdr->msg_len = buf[idx] & 0x3f;
        idx++;
        hdr->somt = (buf[idx] >> 7) & 0x1;
        hdr->eomt = (buf[idx] >> 6) & 0x1;
        hdr->seqno = (buf[idx] >> 4) & 0x1;
        idx++;
        *hdrlen = idx;
        return true;
}

void
drm_dp_encode_sideband_req(const struct drm_dp_sideband_msg_req_body *req,
                           struct drm_dp_sideband_msg_tx *raw)
{
        int idx = 0;
        int i;
        u8 *buf = raw->msg;
        buf[idx++] = req->req_type & 0x7f;

        switch (req->req_type) {
        case DP_ENUM_PATH_RESOURCES:
        case DP_POWER_DOWN_PHY:
        case DP_POWER_UP_PHY:
                buf[idx] = (req->u.port_num.port_number & 0xf) << 4;
                idx++;
                break;
        case DP_ALLOCATE_PAYLOAD:
                buf[idx] = (req->u.allocate_payload.port_number & 0xf) << 4 |
                        (req->u.allocate_payload.number_sdp_streams & 0xf);
                idx++;
                buf[idx] = (req->u.allocate_payload.vcpi & 0x7f);
                idx++;
                buf[idx] = (req->u.allocate_payload.pbn >> 8);
                idx++;
                buf[idx] = (req->u.allocate_payload.pbn & 0xff);
                idx++;
                for (i = 0; i < req->u.allocate_payload.number_sdp_streams / 2; i++) {
                        buf[idx] = ((req->u.allocate_payload.sdp_stream_sink[i * 2] & 0xf) << 4) |
                                (req->u.allocate_payload.sdp_stream_sink[i * 2 + 1] & 0xf);
                        idx++;
                }
                if (req->u.allocate_payload.number_sdp_streams & 1) {
                        i = req->u.allocate_payload.number_sdp_streams - 1;
                        buf[idx] = (req->u.allocate_payload.sdp_stream_sink[i] & 0xf) << 4;
                        idx++;
                }
                break;
        case DP_QUERY_PAYLOAD:
                buf[idx] = (req->u.query_payload.port_number & 0xf) << 4;
                idx++;
                buf[idx] = (req->u.query_payload.vcpi & 0x7f);
                idx++;
                break;
        case DP_REMOTE_DPCD_READ:
                buf[idx] = (req->u.dpcd_read.port_number & 0xf) << 4;
                buf[idx] |= ((req->u.dpcd_read.dpcd_address & 0xf0000) >> 16) & 0xf;
                idx++;
                buf[idx] = (req->u.dpcd_read.dpcd_address & 0xff00) >> 8;
                idx++;
                buf[idx] = (req->u.dpcd_read.dpcd_address & 0xff);
                idx++;
                buf[idx] = (req->u.dpcd_read.num_bytes);
                idx++;
                break;

        case DP_REMOTE_DPCD_WRITE:
                buf[idx] = (req->u.dpcd_write.port_number & 0xf) << 4;
                buf[idx] |= ((req->u.dpcd_write.dpcd_address & 0xf0000) >> 16) & 0xf;
                idx++;
                buf[idx] = (req->u.dpcd_write.dpcd_address & 0xff00) >> 8;
                idx++;
                buf[idx] = (req->u.dpcd_write.dpcd_address & 0xff);
                idx++;
                buf[idx] = (req->u.dpcd_write.num_bytes);
                idx++;
                memcpy(&buf[idx], req->u.dpcd_write.bytes, req->u.dpcd_write.num_bytes);
                idx += req->u.dpcd_write.num_bytes;
                break;
        case DP_REMOTE_I2C_READ:
                buf[idx] = (req->u.i2c_read.port_number & 0xf) << 4;
                buf[idx] |= (req->u.i2c_read.num_transactions & 0x3);
                idx++;
                for (i = 0; i < (req->u.i2c_read.num_transactions & 0x3); i++) {
                        buf[idx] = req->u.i2c_read.transactions[i].i2c_dev_id & 0x7f;
                        idx++;
                        buf[idx] = req->u.i2c_read.transactions[i].num_bytes;
                        idx++;
                        memcpy(&buf[idx], req->u.i2c_read.transactions[i].bytes, req->u.i2c_read.transactions[i].num_bytes);
                        idx += req->u.i2c_read.transactions[i].num_bytes;

                        buf[idx] = (req->u.i2c_read.transactions[i].no_stop_bit & 0x1) << 4;
                        buf[idx] |= (req->u.i2c_read.transactions[i].i2c_transaction_delay & 0xf);
                        idx++;
                }
                buf[idx] = (req->u.i2c_read.read_i2c_device_id) & 0x7f;
                idx++;
                buf[idx] = (req->u.i2c_read.num_bytes_read);
                idx++;
                break;

        case DP_REMOTE_I2C_WRITE:
                buf[idx] = (req->u.i2c_write.port_number & 0xf) << 4;
                idx++;
                buf[idx] = (req->u.i2c_write.write_i2c_device_id) & 0x7f;
                idx++;
                buf[idx] = (req->u.i2c_write.num_bytes);
                idx++;
                memcpy(&buf[idx], req->u.i2c_write.bytes, req->u.i2c_write.num_bytes);
                idx += req->u.i2c_write.num_bytes;
                break;
        }
        raw->cur_len = idx;
}
EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_encode_sideband_req);

/* Decode a sideband request we've encoded, mainly used for debugging */
int
drm_dp_decode_sideband_req(const struct drm_dp_sideband_msg_tx *raw,
                           struct drm_dp_sideband_msg_req_body *req)
{
        const u8 *buf = raw->msg;
        int i, idx = 0;

        req->req_type = buf[idx++] & 0x7f;
        switch (req->req_type) {
        case DP_ENUM_PATH_RESOURCES:
        case DP_POWER_DOWN_PHY:
        case DP_POWER_UP_PHY:
                req->u.port_num.port_number = (buf[idx] >> 4) & 0xf;
                break;
        case DP_ALLOCATE_PAYLOAD:
                {
                        struct drm_dp_allocate_payload *a =
                                &req->u.allocate_payload;

                        a->number_sdp_streams = buf[idx] & 0xf;
                        a->port_number = (buf[idx] >> 4) & 0xf;

                        WARN_ON(buf[++idx] & 0x80);
                        a->vcpi = buf[idx] & 0x7f;

                        a->pbn = buf[++idx] << 8;
                        a->pbn |= buf[++idx];

                        idx++;
                        for (i = 0; i < a->number_sdp_streams; i++) {
                                a->sdp_stream_sink[i] =
                                        (buf[idx + (i / 2)] >> ((i % 2) ? 0 : 4)) & 0xf;
                        }
                }
                break;
        case DP_QUERY_PAYLOAD:
                req->u.query_payload.port_number = (buf[idx] >> 4) & 0xf;
                WARN_ON(buf[++idx] & 0x80);
                req->u.query_payload.vcpi = buf[idx] & 0x7f;
                break;
        case DP_REMOTE_DPCD_READ:
                {
                        struct drm_dp_remote_dpcd_read *r = &req->u.dpcd_read;

                        r->port_number = (buf[idx] >> 4) & 0xf;

                        r->dpcd_address = (buf[idx] << 16) & 0xf0000;
                        r->dpcd_address |= (buf[++idx] << 8) & 0xff00;
                        r->dpcd_address |= buf[++idx] & 0xff;

                        r->num_bytes = buf[++idx];
                }
                break;
        case DP_REMOTE_DPCD_WRITE:
                {
                        struct drm_dp_remote_dpcd_write *w =
                                &req->u.dpcd_write;

                        w->port_number = (buf[idx] >> 4) & 0xf;

                        w->dpcd_address = (buf[idx] << 16) & 0xf0000;
                        w->dpcd_address |= (buf[++idx] << 8) & 0xff00;
                        w->dpcd_address |= buf[++idx] & 0xff;

                        w->num_bytes = buf[++idx];

                        w->bytes = kmemdup(&buf[++idx], w->num_bytes,
                                           GFP_KERNEL);
                        if (!w->bytes)
                                return -ENOMEM;
                }
                break;
        case DP_REMOTE_I2C_READ:
                {
                        struct drm_dp_remote_i2c_read *r = &req->u.i2c_read;
                        struct drm_dp_remote_i2c_read_tx *tx;
                        bool failed = false;

                        r->num_transactions = buf[idx] & 0x3;
                        r->port_number = (buf[idx] >> 4) & 0xf;
                        for (i = 0; i < r->num_transactions; i++) {
                                tx = &r->transactions[i];

                                tx->i2c_dev_id = buf[++idx] & 0x7f;
                                tx->num_bytes = buf[++idx];
                                tx->bytes = kmemdup(&buf[++idx],
                                                    tx->num_bytes,
                                                    GFP_KERNEL);
                                if (!tx->bytes) {
                                        failed = true;
                                        break;
                                }
                                idx += tx->num_bytes;
                                tx->no_stop_bit = (buf[idx] >> 5) & 0x1;
                                tx->i2c_transaction_delay = buf[idx] & 0xf;
                        }

                        if (failed) {
                                for (i = 0; i < r->num_transactions; i++)
                                        kfree(tx->bytes);
                                return -ENOMEM;
                        }

                        r->read_i2c_device_id = buf[++idx] & 0x7f;
                        r->num_bytes_read = buf[++idx];
                }
                break;
        case DP_REMOTE_I2C_WRITE:
                {
                        struct drm_dp_remote_i2c_write *w = &req->u.i2c_write;

                        w->port_number = (buf[idx] >> 4) & 0xf;
                        w->write_i2c_device_id = buf[++idx] & 0x7f;
                        w->num_bytes = buf[++idx];
                        w->bytes = kmemdup(&buf[++idx], w->num_bytes,
                                           GFP_KERNEL);
                        if (!w->bytes)
                                return -ENOMEM;
                }
                break;
        }

        return 0;
}
EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_decode_sideband_req);

void
drm_dp_dump_sideband_msg_req_body(const struct drm_dp_sideband_msg_req_body *req,
                                  int indent, struct drm_printer *printer)
{
        int i;

#define P(f, ...) drm_printf_indent(printer, indent, f, ##__VA_ARGS__)
        if (req->req_type == DP_LINK_ADDRESS) {
                /* No contents to print */
                P("type=%s\n", drm_dp_mst_req_type_str(req->req_type));
                return;
        }

        P("type=%s contents:\n", drm_dp_mst_req_type_str(req->req_type));
        indent++;

        switch (req->req_type) {
        case DP_ENUM_PATH_RESOURCES:
        case DP_POWER_DOWN_PHY:
        case DP_POWER_UP_PHY:
                P("port=%d\n", req->u.port_num.port_number);
                break;
        case DP_ALLOCATE_PAYLOAD:
                P("port=%d vcpi=%d pbn=%d sdp_streams=%d %*ph\n",
                  req->u.allocate_payload.port_number,
                  req->u.allocate_payload.vcpi, req->u.allocate_payload.pbn,
                  req->u.allocate_payload.number_sdp_streams,
                  req->u.allocate_payload.number_sdp_streams,
                  req->u.allocate_payload.sdp_stream_sink);
                break;
        case DP_QUERY_PAYLOAD:
                P("port=%d vcpi=%d\n",
                  req->u.query_payload.port_number,
                  req->u.query_payload.vcpi);
                break;
        case DP_REMOTE_DPCD_READ:
                P("port=%d dpcd_addr=%05x len=%d\n",
                  req->u.dpcd_read.port_number, req->u.dpcd_read.dpcd_address,
                  req->u.dpcd_read.num_bytes);
                break;
        case DP_REMOTE_DPCD_WRITE:
                P("port=%d addr=%05x len=%d: %*ph\n",
                  req->u.dpcd_write.port_number,
                  req->u.dpcd_write.dpcd_address,
                  req->u.dpcd_write.num_bytes, req->u.dpcd_write.num_bytes,
                  req->u.dpcd_write.bytes);
                break;
        case DP_REMOTE_I2C_READ:
                P("port=%d num_tx=%d id=%d size=%d:\n",
                  req->u.i2c_read.port_number,
                  req->u.i2c_read.num_transactions,
                  req->u.i2c_read.read_i2c_device_id,
                  req->u.i2c_read.num_bytes_read);

                indent++;
                for (i = 0; i < req->u.i2c_read.num_transactions; i++) {
                        const struct drm_dp_remote_i2c_read_tx *rtx =
                                &req->u.i2c_read.transactions[i];

                        P("%d: id=%03d size=%03d no_stop_bit=%d tx_delay=%03d: %*ph\n",
                          i, rtx->i2c_dev_id, rtx->num_bytes,
                          rtx->no_stop_bit, rtx->i2c_transaction_delay,
                          rtx->num_bytes, rtx->bytes);
                }
                break;
        case DP_REMOTE_I2C_WRITE:
                P("port=%d id=%d size=%d: %*ph\n",
                  req->u.i2c_write.port_number,
                  req->u.i2c_write.write_i2c_device_id,
                  req->u.i2c_write.num_bytes, req->u.i2c_write.num_bytes,
                  req->u.i2c_write.bytes);
                break;
        default:
                P("???\n");
                break;
        }
#undef P
}
EXPORT_SYMBOL_FOR_TESTS_ONLY(drm_dp_dump_sideband_msg_req_body);

static inline void
drm_dp_mst_dump_sideband_msg_tx(struct drm_printer *p,
                                const struct drm_dp_sideband_msg_tx *txmsg)
{
        struct drm_dp_sideband_msg_req_body req;
        char buf[64];
        int ret;
        int i;

        drm_dp_mst_rad_to_str(txmsg->dst->rad, txmsg->dst->lct, buf,
                              sizeof(buf));
        drm_printf(p, "txmsg cur_offset=%x cur_len=%x seqno=%x state=%s path_msg=%d dst=%s\n",
                   txmsg->cur_offset, txmsg->cur_len, txmsg->seqno,
                   drm_dp_mst_sideband_tx_state_str(txmsg->state),
                   txmsg->path_msg, buf);

        ret = drm_dp_decode_sideband_req(txmsg, &req);
        if (ret) {
                drm_printf(p, "<failed to decode sideband req: %d>\n", ret);
                return;
        }
        drm_dp_dump_sideband_msg_req_body(&req, 1, p);

        switch (req.req_type) {
        case DP_REMOTE_DPCD_WRITE:
                kfree(req.u.dpcd_write.bytes);
                break;
        case DP_REMOTE_I2C_READ:
                for (i = 0; i < req.u.i2c_read.num_transactions; i++)
                        kfree(req.u.i2c_read.transactions[i].bytes);
                break;
        case DP_REMOTE_I2C_WRITE:
                kfree(req.u.i2c_write.bytes);
                break;
        }
}

static void drm_dp_crc_sideband_chunk_req(u8 *msg, u8 len)
{
        u8 crc4;
        crc4 = drm_dp_msg_data_crc4(msg, len);
        msg[len] = crc4;
}

static void drm_dp_encode_sideband_reply(struct drm_dp_sideband_msg_reply_body *rep,
                                         struct drm_dp_sideband_msg_tx *raw)
{
        int idx = 0;
        u8 *buf = raw->msg;

        buf[idx++] = (rep->reply_type & 0x1) << 7 | (rep->req_type & 0x7f);

        raw->cur_len = idx;
}

/* this adds a chunk of msg to the builder to get the final msg */
static bool drm_dp_sideband_msg_build(struct drm_dp_sideband_msg_rx *msg,
                                      u8 *replybuf, u8 replybuflen, bool hdr)
{
        int ret;
        u8 crc4;

        if (hdr) {
                u8 hdrlen;
                struct drm_dp_sideband_msg_hdr recv_hdr;
                ret = drm_dp_decode_sideband_msg_hdr(&recv_hdr, replybuf, replybuflen, &hdrlen);
                if (ret == false) {
                        print_hex_dump(KERN_DEBUG, "failed hdr", DUMP_PREFIX_NONE, 16, 1, replybuf, replybuflen, false);
                        return false;
                }

                /*
                 * ignore out-of-order messages or messages that are part of a
                 * failed transaction
                 */
                if (!recv_hdr.somt && !msg->have_somt)
                        return false;

                /* get length contained in this portion */
                msg->curchunk_len = recv_hdr.msg_len;
                msg->curchunk_hdrlen = hdrlen;

                /* we have already gotten an somt - don't bother parsing */
                if (recv_hdr.somt && msg->have_somt)
                        return false;

                if (recv_hdr.somt) {
                        memcpy(&msg->initial_hdr, &recv_hdr, sizeof(struct drm_dp_sideband_msg_hdr));
                        msg->have_somt = true;
                }
                if (recv_hdr.eomt)
                        msg->have_eomt = true;

                /* copy the bytes for the remainder of this header chunk */
                msg->curchunk_idx = min(msg->curchunk_len, (u8)(replybuflen - hdrlen));
                memcpy(&msg->chunk[0], replybuf + hdrlen, msg->curchunk_idx);
        } else {
                memcpy(&msg->chunk[msg->curchunk_idx], replybuf, replybuflen);
                msg->curchunk_idx += replybuflen;
        }

        if (msg->curchunk_idx >= msg->curchunk_len) {
                /* do CRC */
                crc4 = drm_dp_msg_data_crc4(msg->chunk, msg->curchunk_len - 1);
                /* copy chunk into bigger msg */
                memcpy(&msg->msg[msg->curlen], msg->chunk, msg->curchunk_len - 1);
                msg->curlen += msg->curchunk_len - 1;
        }
        return true;
}

static bool drm_dp_sideband_parse_link_address(struct drm_dp_sideband_msg_rx *raw,
                                               struct drm_dp_sideband_msg_reply_body *repmsg)
{
        int idx = 1;
        int i;
        memcpy(repmsg->u.link_addr.guid, &raw->msg[idx], 16);
        idx += 16;
        repmsg->u.link_addr.nports = raw->msg[idx] & 0xf;
        idx++;
        if (idx > raw->curlen)
                goto fail_len;
        for (i = 0; i < repmsg->u.link_addr.nports; i++) {
                if (raw->msg[idx] & 0x80)
                        repmsg->u.link_addr.ports[i].input_port = 1;

                repmsg->u.link_addr.ports[i].peer_device_type = (raw->msg[idx] >> 4) & 0x7;
                repmsg->u.link_addr.ports[i].port_number = (raw->msg[idx] & 0xf);

                idx++;
                if (idx > raw->curlen)
                        goto fail_len;
                repmsg->u.link_addr.ports[i].mcs = (raw->msg[idx] >> 7) & 0x1;
                repmsg->u.link_addr.ports[i].ddps = (raw->msg[idx] >> 6) & 0x1;
                if (repmsg->u.link_addr.ports[i].input_port == 0)
                        repmsg->u.link_addr.ports[i].legacy_device_plug_status = (raw->msg[idx] >> 5) & 0x1;
                idx++;
                if (idx > raw->curlen)
                        goto fail_len;
                if (repmsg->u.link_addr.ports[i].input_port == 0) {
                        repmsg->u.link_addr.ports[i].dpcd_revision = (raw->msg[idx]);
                        idx++;
                        if (idx > raw->curlen)
                                goto fail_len;
                        memcpy(repmsg->u.link_addr.ports[i].peer_guid, &raw->msg[idx], 16);
                        idx += 16;
                        if (idx > raw->curlen)
                                goto fail_len;
                        repmsg->u.link_addr.ports[i].num_sdp_streams = (raw->msg[idx] >> 4) & 0xf;
                        repmsg->u.link_addr.ports[i].num_sdp_stream_sinks = (raw->msg[idx] & 0xf);
                        idx++;

                }
                if (idx > raw->curlen)
                        goto fail_len;
        }

        return true;
fail_len:
        DRM_DEBUG_KMS("link address reply parse length fail %d %d\n", idx, raw->curlen);
        return false;
}

static bool drm_dp_sideband_parse_remote_dpcd_read(struct drm_dp_sideband_msg_rx *raw,
                                                   struct drm_dp_sideband_msg_reply_body *repmsg)
{
        int idx = 1;
        repmsg->u.remote_dpcd_read_ack.port_number = raw->msg[idx] & 0xf;
        idx++;
        if (idx > raw->curlen)
                goto fail_len;
        repmsg->u.remote_dpcd_read_ack.num_bytes = raw->msg[idx];
        idx++;
        if (idx > raw->curlen)
                goto fail_len;

        memcpy(repmsg->u.remote_dpcd_read_ack.bytes, &raw->msg[idx], repmsg->u.remote_dpcd_read_ack.num_bytes);
        return true;
fail_len:
        DRM_DEBUG_KMS("link address reply parse length fail %d %d\n", idx, raw->curlen);
        return false;
}

static bool drm_dp_sideband_parse_remote_dpcd_write(struct drm_dp_sideband_msg_rx *raw,
                                                      struct drm_dp_sideband_msg_reply_body *repmsg)
{
        int idx = 1;
        repmsg->u.remote_dpcd_write_ack.port_number = raw->msg[idx] & 0xf;
        idx++;
        if (idx > raw->curlen)
                goto fail_len;
        return true;
fail_len:
        DRM_DEBUG_KMS("parse length fail %d %d\n", idx, raw->curlen);
        return false;
}

static bool drm_dp_sideband_parse_remote_i2c_read_ack(struct drm_dp_sideband_msg_rx *raw,
                                                      struct drm_dp_sideband_msg_reply_body *repmsg)
{
        int idx = 1;

        repmsg->u.remote_i2c_read_ack.port_number = (raw->msg[idx] & 0xf);
        idx++;
        if (idx > raw->curlen)
                goto fail_len;
        repmsg->u.remote_i2c_read_ack.num_bytes = raw->msg[idx];
        idx++;
        /* TODO check */
        memcpy(repmsg->u.remote_i2c_read_ack.bytes, &raw->msg[idx], repmsg->u.remote_i2c_read_ack.num_bytes);
        return true;
fail_len:
        DRM_DEBUG_KMS("remote i2c reply parse length fail %d %d\n", idx, raw->curlen);
        return false;
}

static bool drm_dp_sideband_parse_enum_path_resources_ack(struct drm_dp_sideband_msg_rx *raw,
                                                          struct drm_dp_sideband_msg_reply_body *repmsg)
{
        int idx = 1;
        repmsg->u.path_resources.port_number = (raw->msg[idx] >> 4) & 0xf;
        idx++;
        if (idx > raw->curlen)
                goto fail_len;
        repmsg->u.path_resources.full_payload_bw_number = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
        idx += 2;
        if (idx > raw->curlen)
                goto fail_len;
        repmsg->u.path_resources.avail_payload_bw_number = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
        idx += 2;
        if (idx > raw->curlen)
                goto fail_len;
        return true;
fail_len:
        DRM_DEBUG_KMS("enum resource parse length fail %d %d\n", idx, raw->curlen);
        return false;
}

static bool drm_dp_sideband_parse_allocate_payload_ack(struct drm_dp_sideband_msg_rx *raw,
                                                          struct drm_dp_sideband_msg_reply_body *repmsg)
{
        int idx = 1;
        repmsg->u.allocate_payload.port_number = (raw->msg[idx] >> 4) & 0xf;
        idx++;
        if (idx > raw->curlen)
                goto fail_len;
        repmsg->u.allocate_payload.vcpi = raw->msg[idx];
        idx++;
        if (idx > raw->curlen)
                goto fail_len;
        repmsg->u.allocate_payload.allocated_pbn = (raw->msg[idx] << 8) | (raw->msg[idx+1]);
        idx += 2;
        if (idx > raw->curlen)
                goto fail_len;
        return true;
fail_len:
        DRM_DEBUG_KMS("allocate payload parse length fail %d %d\n", idx, raw->curlen);
        return false;
}

static bool drm_dp_sideband_parse_query_payload_ack(struct drm_dp_sideband_msg_rx *raw,
                                                    struct drm_dp_sideband_msg_reply_body *repmsg)
{
        int idx = 1;
        repmsg->u.query_payload.port_number = (raw->msg[idx] >> 4) & 0xf;
        idx++;
        if (idx > raw->curlen)
                goto fail_len;
        repmsg->u.query_payload.allocated_pbn = (raw->msg[idx] << 8) | (raw->msg[idx + 1]);
        idx += 2;
        if (idx > raw->curlen)
                goto fail_len;
        return true;
fail_len:
        DRM_DEBUG_KMS("query payload parse length fail %d %d\n", idx, raw->curlen);
        return false;
}

static bool drm_dp_sideband_parse_power_updown_phy_ack(struct drm_dp_sideband_msg_rx *raw,
                                                       struct drm_dp_sideband_msg_reply_body *repmsg)
{
        int idx = 1;

        repmsg->u.port_number.port_number = (raw->msg[idx] >> 4) & 0xf;
        idx++;
        if (idx > raw->curlen) {
                DRM_DEBUG_KMS("power up/down phy parse length fail %d %d\n",
                              idx, raw->curlen);
                return false;
        }
        return true;
}

static bool drm_dp_sideband_parse_reply(struct drm_dp_sideband_msg_rx *raw,
                                        struct drm_dp_sideband_msg_reply_body *msg)
{
        memset(msg, 0, sizeof(*msg));
        msg->reply_type = (raw->msg[0] & 0x80) >> 7;
        msg->req_type = (raw->msg[0] & 0x7f);

        if (msg->reply_type == DP_SIDEBAND_REPLY_NAK) {
                memcpy(msg->u.nak.guid, &raw->msg[1], 16);
                msg->u.nak.reason = raw->msg[17];
                msg->u.nak.nak_data = raw->msg[18];
                return false;
        }

        switch (msg->req_type) {
        case DP_LINK_ADDRESS:
                return drm_dp_sideband_parse_link_address(raw, msg);
        case DP_QUERY_PAYLOAD:
                return drm_dp_sideband_parse_query_payload_ack(raw, msg);
        case DP_REMOTE_DPCD_READ:
                return drm_dp_sideband_parse_remote_dpcd_read(raw, msg);
        case DP_REMOTE_DPCD_WRITE:
                return drm_dp_sideband_parse_remote_dpcd_write(raw, msg);
        case DP_REMOTE_I2C_READ:
                return drm_dp_sideband_parse_remote_i2c_read_ack(raw, msg);
        case DP_ENUM_PATH_RESOURCES:
                return drm_dp_sideband_parse_enum_path_resources_ack(raw, msg);
        case DP_ALLOCATE_PAYLOAD:
                return drm_dp_sideband_parse_allocate_payload_ack(raw, msg);
        case DP_POWER_DOWN_PHY:
        case DP_POWER_UP_PHY:
                return drm_dp_sideband_parse_power_updown_phy_ack(raw, msg);
        default:
                DRM_ERROR("Got unknown reply 0x%02x (%s)\n", msg->req_type,
                          drm_dp_mst_req_type_str(msg->req_type));
                return false;
        }
}

static bool drm_dp_sideband_parse_connection_status_notify(struct drm_dp_sideband_msg_rx *raw,
                                                           struct drm_dp_sideband_msg_req_body *msg)
{
        int idx = 1;

        msg->u.conn_stat.port_number = (raw->msg[idx] & 0xf0) >> 4;
        idx++;
        if (idx > raw->curlen)
                goto fail_len;

        memcpy(msg->u.conn_stat.guid, &raw->msg[idx], 16);
        idx += 16;
        if (idx > raw->curlen)
                goto fail_len;

        msg->u.conn_stat.legacy_device_plug_status = (raw->msg[idx] >> 6) & 0x1;
        msg->u.conn_stat.displayport_device_plug_status = (raw->msg[idx] >> 5) & 0x1;
        msg->u.conn_stat.message_capability_status = (raw->msg[idx] >> 4) & 0x1;
        msg->u.conn_stat.input_port = (raw->msg[idx] >> 3) & 0x1;
        msg->u.conn_stat.peer_device_type = (raw->msg[idx] & 0x7);
        idx++;
        return true;
fail_len:
        DRM_DEBUG_KMS("connection status reply parse length fail %d %d\n", idx, raw->curlen);
        return false;
}

static bool drm_dp_sideband_parse_resource_status_notify(struct drm_dp_sideband_msg_rx *raw,
                                                           struct drm_dp_sideband_msg_req_body *msg)
{
        int idx = 1;

        msg->u.resource_stat.port_number = (raw->msg[idx] & 0xf0) >> 4;
        idx++;
        if (idx > raw->curlen)
                goto fail_len;

        memcpy(msg->u.resource_stat.guid, &raw->msg[idx], 16);
        idx += 16;
        if (idx > raw->curlen)
                goto fail_len;

        msg->u.resource_stat.available_pbn = (raw->msg[idx] << 8) | (raw->msg[idx + 1]);
        idx++;
        return true;
fail_len:
        DRM_DEBUG_KMS("resource status reply parse length fail %d %d\n", idx, raw->curlen);
        return false;
}

static bool drm_dp_sideband_parse_req(struct drm_dp_sideband_msg_rx *raw,
                                      struct drm_dp_sideband_msg_req_body *msg)
{
        memset(msg, 0, sizeof(*msg));
        msg->req_type = (raw->msg[0] & 0x7f);

        switch (msg->req_type) {
        case DP_CONNECTION_STATUS_NOTIFY:
                return drm_dp_sideband_parse_connection_status_notify(raw, msg);
        case DP_RESOURCE_STATUS_NOTIFY:
                return drm_dp_sideband_parse_resource_status_notify(raw, msg);
        default:
                DRM_ERROR("Got unknown request 0x%02x (%s)\n", msg->req_type,
                          drm_dp_mst_req_type_str(msg->req_type));
                return false;
        }
}

static int build_dpcd_write(struct drm_dp_sideband_msg_tx *msg, u8 port_num, u32 offset, u8 num_bytes, u8 *bytes)
{
        struct drm_dp_sideband_msg_req_body req;

        req.req_type = DP_REMOTE_DPCD_WRITE;
        req.u.dpcd_write.port_number = port_num;
        req.u.dpcd_write.dpcd_address = offset;
        req.u.dpcd_write.num_bytes = num_bytes;
        req.u.dpcd_write.bytes = bytes;
        drm_dp_encode_sideband_req(&req, msg);

        return 0;
}

static int build_link_address(struct drm_dp_sideband_msg_tx *msg)
{
        struct drm_dp_sideband_msg_req_body req;

        req.req_type = DP_LINK_ADDRESS;
        drm_dp_encode_sideband_req(&req, msg);
        return 0;
}

static int build_enum_path_resources(struct drm_dp_sideband_msg_tx *msg, int port_num)
{
        struct drm_dp_sideband_msg_req_body req;

        req.req_type = DP_ENUM_PATH_RESOURCES;
        req.u.port_num.port_number = port_num;
        drm_dp_encode_sideband_req(&req, msg);
        msg->path_msg = true;
        return 0;
}

static int build_allocate_payload(struct drm_dp_sideband_msg_tx *msg, int port_num,
                                  u8 vcpi, uint16_t pbn,
                                  u8 number_sdp_streams,
                                  u8 *sdp_stream_sink)
{
        struct drm_dp_sideband_msg_req_body req;
        memset(&req, 0, sizeof(req));
        req.req_type = DP_ALLOCATE_PAYLOAD;
        req.u.allocate_payload.port_number = port_num;
        req.u.allocate_payload.vcpi = vcpi;
        req.u.allocate_payload.pbn = pbn;
        req.u.allocate_payload.number_sdp_streams = number_sdp_streams;
        memcpy(req.u.allocate_payload.sdp_stream_sink, sdp_stream_sink,
                   number_sdp_streams);
        drm_dp_encode_sideband_req(&req, msg);
        msg->path_msg = true;
        return 0;
}

static int build_power_updown_phy(struct drm_dp_sideband_msg_tx *msg,
                                  int port_num, bool power_up)
{
        struct drm_dp_sideband_msg_req_body req;

        if (power_up)
                req.req_type = DP_POWER_UP_PHY;
        else
                req.req_type = DP_POWER_DOWN_PHY;

        req.u.port_num.port_number = port_num;
        drm_dp_encode_sideband_req(&req, msg);
        msg->path_msg = true;
        return 0;
}

static int drm_dp_mst_assign_payload_id(struct drm_dp_mst_topology_mgr *mgr,
                                        struct drm_dp_vcpi *vcpi)
{
        int ret, vcpi_ret;

        mutex_lock(&mgr->payload_lock);
        ret = find_first_zero_bit(&mgr->payload_mask, mgr->max_payloads + 1);
        if (ret > mgr->max_payloads) {
                ret = -EINVAL;
                DRM_DEBUG_KMS("out of payload ids %d\n", ret);
                goto out_unlock;
        }

        vcpi_ret = find_first_zero_bit(&mgr->vcpi_mask, mgr->max_payloads + 1);
        if (vcpi_ret > mgr->max_payloads) {
                ret = -EINVAL;
                DRM_DEBUG_KMS("out of vcpi ids %d\n", ret);
                goto out_unlock;
        }

        set_bit(ret, &mgr->payload_mask);
        set_bit(vcpi_ret, &mgr->vcpi_mask);
        vcpi->vcpi = vcpi_ret + 1;
        mgr->proposed_vcpis[ret - 1] = vcpi;
out_unlock:
        mutex_unlock(&mgr->payload_lock);
        return ret;
}

static void drm_dp_mst_put_payload_id(struct drm_dp_mst_topology_mgr *mgr,
                                      int vcpi)
{
        int i;
        if (vcpi == 0)
                return;

        mutex_lock(&mgr->payload_lock);
        DRM_DEBUG_KMS("putting payload %d\n", vcpi);
        clear_bit(vcpi - 1, &mgr->vcpi_mask);

        for (i = 0; i < mgr->max_payloads; i++) {
                if (mgr->proposed_vcpis[i] &&
                    mgr->proposed_vcpis[i]->vcpi == vcpi) {
                        mgr->proposed_vcpis[i] = NULL;
                        clear_bit(i + 1, &mgr->payload_mask);
                }
        }
        mutex_unlock(&mgr->payload_lock);
}

static bool check_txmsg_state(struct drm_dp_mst_topology_mgr *mgr,
                              struct drm_dp_sideband_msg_tx *txmsg)
{
        unsigned int state;

        /*
         * All updates to txmsg->state are protected by mgr->qlock, and the two
         * cases we check here are terminal states. For those the barriers
         * provided by the wake_up/wait_event pair are enough.
         */
        state = READ_ONCE(txmsg->state);
        return (state == DRM_DP_SIDEBAND_TX_RX ||
                state == DRM_DP_SIDEBAND_TX_TIMEOUT);
}

static int drm_dp_mst_wait_tx_reply(struct drm_dp_mst_branch *mstb,
                                    struct drm_dp_sideband_msg_tx *txmsg)
{
        struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
        int ret;

        ret = wait_event_timeout(mgr->tx_waitq,
                                 check_txmsg_state(mgr, txmsg),
                                 (4 * HZ));
        mutex_lock(&mstb->mgr->qlock);
        if (ret > 0) {
                if (txmsg->state == DRM_DP_SIDEBAND_TX_TIMEOUT) {
                        ret = -EIO;
                        goto out;
                }
        } else {
                DRM_DEBUG_KMS("timedout msg send %p %d %d\n", txmsg, txmsg->state, txmsg->seqno);

                /* dump some state */
                ret = -EIO;

                /* remove from q */
                if (txmsg->state == DRM_DP_SIDEBAND_TX_QUEUED ||
                    txmsg->state == DRM_DP_SIDEBAND_TX_START_SEND) {
                        list_del(&txmsg->next);
                }

                if (txmsg->state == DRM_DP_SIDEBAND_TX_START_SEND ||
                    txmsg->state == DRM_DP_SIDEBAND_TX_SENT) {
                        mstb->tx_slots[txmsg->seqno] = NULL;
                }
                mgr->is_waiting_for_dwn_reply = false;

        }
out:
        if (unlikely(ret == -EIO) && drm_debug_enabled(DRM_UT_DP)) {
                struct drm_printer p = drm_debug_printer(DBG_PREFIX);

                drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
        }
        mutex_unlock(&mgr->qlock);

        drm_dp_mst_kick_tx(mgr);
        return ret;
}

static struct drm_dp_mst_branch *drm_dp_add_mst_branch_device(u8 lct, u8 *rad)
{
        struct drm_dp_mst_branch *mstb;

        mstb = kzalloc(sizeof(*mstb), GFP_KERNEL);
        if (!mstb)
                return NULL;

        mstb->lct = lct;
        if (lct > 1)
                memcpy(mstb->rad, rad, lct / 2);
        INIT_LIST_HEAD(&mstb->ports);
        kref_init(&mstb->topology_kref);
        kref_init(&mstb->malloc_kref);
        return mstb;
}

static void drm_dp_free_mst_branch_device(struct kref *kref)
{
        struct drm_dp_mst_branch *mstb =
                container_of(kref, struct drm_dp_mst_branch, malloc_kref);

        if (mstb->port_parent)
                drm_dp_mst_put_port_malloc(mstb->port_parent);

        kfree(mstb);
}

/**
 * DOC: Branch device and port refcounting
 *
 * Topology refcount overview
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * The refcounting schemes for &struct drm_dp_mst_branch and &struct
 * drm_dp_mst_port are somewhat unusual. Both ports and branch devices have
 * two different kinds of refcounts: topology refcounts, and malloc refcounts.
 *
 * Topology refcounts are not exposed to drivers, and are handled internally
 * by the DP MST helpers. The helpers use them in order to prevent the
 * in-memory topology state from being changed in the middle of critical
 * operations like changing the internal state of payload allocations. This
 * means each branch and port will be considered to be connected to the rest
 * of the topology until its topology refcount reaches zero. Additionally,
 * for ports this means that their associated &struct drm_connector will stay
 * registered with userspace until the port's refcount reaches 0.
 *
 * Malloc refcount overview
 * ~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * Malloc references are used to keep a &struct drm_dp_mst_port or &struct
 * drm_dp_mst_branch allocated even after all of its topology references have
 * been dropped, so that the driver or MST helpers can safely access each
 * branch's last known state before it was disconnected from the topology.
 * When the malloc refcount of a port or branch reaches 0, the memory
 * allocation containing the &struct drm_dp_mst_branch or &struct
 * drm_dp_mst_port respectively will be freed.
 *
 * For &struct drm_dp_mst_branch, malloc refcounts are not currently exposed
 * to drivers. As of writing this documentation, there are no drivers that
 * have a usecase for accessing &struct drm_dp_mst_branch outside of the MST
 * helpers. Exposing this API to drivers in a race-free manner would take more
 * tweaking of the refcounting scheme, however patches are welcome provided
 * there is a legitimate driver usecase for this.
 *
 * Refcount relationships in a topology
 * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 *
 * Let's take a look at why the relationship between topology and malloc
 * refcounts is designed the way it is.
 *
 * .. kernel-figure:: dp-mst/topology-figure-1.dot
 *
 *    An example of topology and malloc refs in a DP MST topology with two
 *    active payloads. Topology refcount increments are indicated by solid
 *    lines, and malloc refcount increments are indicated by dashed lines.
 *    Each starts from the branch which incremented the refcount, and ends at
 *    the branch to which the refcount belongs to, i.e. the arrow points the
 *    same way as the C pointers used to reference a structure.
 *
 * As you can see in the above figure, every branch increments the topology
 * refcount of its children, and increments the malloc refcount of its
 * parent. Additionally, every payload increments the malloc refcount of its
 * assigned port by 1.
 *
 * So, what would happen if MSTB #3 from the above figure was unplugged from
 * the system, but the driver hadn't yet removed payload #2 from port #3? The
 * topology would start to look like the figure below.
 *
 * .. kernel-figure:: dp-mst/topology-figure-2.dot
 *
 *    Ports and branch devices which have been released from memory are
 *    colored grey, and references which have been removed are colored red.
 *
 * Whenever a port or branch device's topology refcount reaches zero, it will
 * decrement the topology refcounts of all its children, the malloc refcount
 * of its parent, and finally its own malloc refcount. For MSTB #4 and port
 * #4, this means they both have been disconnected from the topology and freed
 * from memory. But, because payload #2 is still holding a reference to port
 * #3, port #3 is removed from the topology but its &struct drm_dp_mst_port
 * is still accessible from memory. This also means port #3 has not yet
 * decremented the malloc refcount of MSTB #3, so its &struct
 * drm_dp_mst_branch will also stay allocated in memory until port #3's
 * malloc refcount reaches 0.
 *
 * This relationship is necessary because in order to release payload #2, we
 * need to be able to figure out the last relative of port #3 that's still
 * connected to the topology. In this case, we would travel up the topology as
 * shown below.
 *
 * .. kernel-figure:: dp-mst/topology-figure-3.dot
 *
 * And finally, remove payload #2 by communicating with port #2 through
 * sideband transactions.
 */

/**
 * drm_dp_mst_get_mstb_malloc() - Increment the malloc refcount of a branch
 * device
 * @mstb: The &struct drm_dp_mst_branch to increment the malloc refcount of
 *
 * Increments &drm_dp_mst_branch.malloc_kref. When
 * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
 * will be released and @mstb may no longer be used.
 *
 * See also: drm_dp_mst_put_mstb_malloc()
 */
static void
drm_dp_mst_get_mstb_malloc(struct drm_dp_mst_branch *mstb)
{
        kref_get(&mstb->malloc_kref);
        DRM_DEBUG("mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref));
}

/**
 * drm_dp_mst_put_mstb_malloc() - Decrement the malloc refcount of a branch
 * device
 * @mstb: The &struct drm_dp_mst_branch to decrement the malloc refcount of
 *
 * Decrements &drm_dp_mst_branch.malloc_kref. When
 * &drm_dp_mst_branch.malloc_kref reaches 0, the memory allocation for @mstb
 * will be released and @mstb may no longer be used.
 *
 * See also: drm_dp_mst_get_mstb_malloc()
 */
static void
drm_dp_mst_put_mstb_malloc(struct drm_dp_mst_branch *mstb)
{
        DRM_DEBUG("mstb %p (%d)\n", mstb, kref_read(&mstb->malloc_kref) - 1);
        kref_put(&mstb->malloc_kref, drm_dp_free_mst_branch_device);
}

static void drm_dp_free_mst_port(struct kref *kref)
{
        struct drm_dp_mst_port *port =
                container_of(kref, struct drm_dp_mst_port, malloc_kref);

        drm_dp_mst_put_mstb_malloc(port->parent);
        kfree(port);
}

/**
 * drm_dp_mst_get_port_malloc() - Increment the malloc refcount of an MST port
 * @port: The &struct drm_dp_mst_port to increment the malloc refcount of
 *
 * Increments &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
 * reaches 0, the memory allocation for @port will be released and @port may
 * no longer be used.
 *
 * Because @port could potentially be freed at any time by the DP MST helpers
 * if &drm_dp_mst_port.malloc_kref reaches 0, including during a call to this
 * function, drivers that which to make use of &struct drm_dp_mst_port should
 * ensure that they grab at least one main malloc reference to their MST ports
 * in &drm_dp_mst_topology_cbs.add_connector. This callback is called before
 * there is any chance for &drm_dp_mst_port.malloc_kref to reach 0.
 *
 * See also: drm_dp_mst_put_port_malloc()
 */
void
drm_dp_mst_get_port_malloc(struct drm_dp_mst_port *port)
{
        kref_get(&port->malloc_kref);
        DRM_DEBUG("port %p (%d)\n", port, kref_read(&port->malloc_kref));
}
EXPORT_SYMBOL(drm_dp_mst_get_port_malloc);

/**
 * drm_dp_mst_put_port_malloc() - Decrement the malloc refcount of an MST port
 * @port: The &struct drm_dp_mst_port to decrement the malloc refcount of
 *
 * Decrements &drm_dp_mst_port.malloc_kref. When &drm_dp_mst_port.malloc_kref
 * reaches 0, the memory allocation for @port will be released and @port may
 * no longer be used.
 *
 * See also: drm_dp_mst_get_port_malloc()
 */
void
drm_dp_mst_put_port_malloc(struct drm_dp_mst_port *port)
{
        DRM_DEBUG("port %p (%d)\n", port, kref_read(&port->malloc_kref) - 1);
        kref_put(&port->malloc_kref, drm_dp_free_mst_port);
}
EXPORT_SYMBOL(drm_dp_mst_put_port_malloc);

#if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)

#define STACK_DEPTH 8

static noinline void
__topology_ref_save(struct drm_dp_mst_topology_mgr *mgr,
                    struct drm_dp_mst_topology_ref_history *history,
                    enum drm_dp_mst_topology_ref_type type)
{
        struct drm_dp_mst_topology_ref_entry *entry = NULL;
        depot_stack_handle_t backtrace;
        ulong stack_entries[STACK_DEPTH];
        uint n;
        int i;

        n = stack_trace_save(stack_entries, ARRAY_SIZE(stack_entries), 1);
        backtrace = stack_depot_save(stack_entries, n, GFP_KERNEL);
        if (!backtrace)
                return;

        /* Try to find an existing entry for this backtrace */
        for (i = 0; i < history->len; i++) {
                if (history->entries[i].backtrace == backtrace) {
                        entry = &history->entries[i];
                        break;
                }
        }

        /* Otherwise add one */
        if (!entry) {
                struct drm_dp_mst_topology_ref_entry *new;
                int new_len = history->len + 1;

                new = krealloc(history->entries, sizeof(*new) * new_len,
                               GFP_KERNEL);
                if (!new)
                        return;

                entry = &new[history->len];
                history->len = new_len;
                history->entries = new;

                entry->backtrace = backtrace;
                entry->type = type;
                entry->count = 0;
        }
        entry->count++;
        entry->ts_nsec = ktime_get_ns();
}

static int
topology_ref_history_cmp(const void *a, const void *b)
{
        const struct drm_dp_mst_topology_ref_entry *entry_a = a, *entry_b = b;

        if (entry_a->ts_nsec > entry_b->ts_nsec)
                return 1;
        else if (entry_a->ts_nsec < entry_b->ts_nsec)
                return -1;
        else
                return 0;
}

static inline const char *
topology_ref_type_to_str(enum drm_dp_mst_topology_ref_type type)
{
        if (type == DRM_DP_MST_TOPOLOGY_REF_GET)
                return "get";
        else
                return "put";
}

static void
__dump_topology_ref_history(struct drm_dp_mst_topology_ref_history *history,
                            void *ptr, const char *type_str)
{
        struct drm_printer p = drm_debug_printer(DBG_PREFIX);
        char *buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
        int i;

        if (!buf)
                return;

        if (!history->len)
                goto out;

        /* First, sort the list so that it goes from oldest to newest
         * reference entry
         */
        sort(history->entries, history->len, sizeof(*history->entries),
             topology_ref_history_cmp, NULL);

        drm_printf(&p, "%s (%p) topology count reached 0, dumping history:\n",
                   type_str, ptr);

        for (i = 0; i < history->len; i++) {
                const struct drm_dp_mst_topology_ref_entry *entry =
                        &history->entries[i];
                ulong *entries;
                uint nr_entries;
                u64 ts_nsec = entry->ts_nsec;
                u32 rem_nsec = do_div(ts_nsec, 1000000000);

                nr_entries = stack_depot_fetch(entry->backtrace, &entries);
                stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, 4);

                drm_printf(&p, "  %d %ss (last at %5llu.%06u):\n%s",
                           entry->count,
                           topology_ref_type_to_str(entry->type),
                           ts_nsec, rem_nsec / 1000, buf);
        }

        /* Now free the history, since this is the only time we expose it */
        kfree(history->entries);
out:
        kfree(buf);
}

static __always_inline void
drm_dp_mst_dump_mstb_topology_history(struct drm_dp_mst_branch *mstb)
{
        __dump_topology_ref_history(&mstb->topology_ref_history, mstb,
                                    "MSTB");
}

static __always_inline void
drm_dp_mst_dump_port_topology_history(struct drm_dp_mst_port *port)
{
        __dump_topology_ref_history(&port->topology_ref_history, port,
                                    "Port");
}

static __always_inline void
save_mstb_topology_ref(struct drm_dp_mst_branch *mstb,
                       enum drm_dp_mst_topology_ref_type type)
{
        __topology_ref_save(mstb->mgr, &mstb->topology_ref_history, type);
}

static __always_inline void
save_port_topology_ref(struct drm_dp_mst_port *port,
                       enum drm_dp_mst_topology_ref_type type)
{
        __topology_ref_save(port->mgr, &port->topology_ref_history, type);
}

static inline void
topology_ref_history_lock(struct drm_dp_mst_topology_mgr *mgr)
{
        mutex_lock(&mgr->topology_ref_history_lock);
}

static inline void
topology_ref_history_unlock(struct drm_dp_mst_topology_mgr *mgr)
{
        mutex_unlock(&mgr->topology_ref_history_lock);
}
#else
static inline void
topology_ref_history_lock(struct drm_dp_mst_topology_mgr *mgr) {}
static inline void
topology_ref_history_unlock(struct drm_dp_mst_topology_mgr *mgr) {}
static inline void
drm_dp_mst_dump_mstb_topology_history(struct drm_dp_mst_branch *mstb) {}
static inline void
drm_dp_mst_dump_port_topology_history(struct drm_dp_mst_port *port) {}
#define save_mstb_topology_ref(mstb, type)
#define save_port_topology_ref(port, type)
#endif

static void drm_dp_destroy_mst_branch_device(struct kref *kref)
{
        struct drm_dp_mst_branch *mstb =
                container_of(kref, struct drm_dp_mst_branch, topology_kref);
        struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;

        drm_dp_mst_dump_mstb_topology_history(mstb);

        INIT_LIST_HEAD(&mstb->destroy_next);

        /*
         * This can get called under mgr->mutex, so we need to perform the
         * actual destruction of the mstb in another worker
         */
        mutex_lock(&mgr->delayed_destroy_lock);
        list_add(&mstb->destroy_next, &mgr->destroy_branch_device_list);
        mutex_unlock(&mgr->delayed_destroy_lock);
        schedule_work(&mgr->delayed_destroy_work);
}

/**
 * drm_dp_mst_topology_try_get_mstb() - Increment the topology refcount of a
 * branch device unless it's zero
 * @mstb: &struct drm_dp_mst_branch to increment the topology refcount of
 *
 * Attempts to grab a topology reference to @mstb, if it hasn't yet been
 * removed from the topology (e.g. &drm_dp_mst_branch.topology_kref has
 * reached 0). Holding a topology reference implies that a malloc reference
 * will be held to @mstb as long as the user holds the topology reference.
 *
 * Care should be taken to ensure that the user has at least one malloc
 * reference to @mstb. If you already have a topology reference to @mstb, you
 * should use drm_dp_mst_topology_get_mstb() instead.
 *
 * See also:
 * drm_dp_mst_topology_get_mstb()
 * drm_dp_mst_topology_put_mstb()
 *
 * Returns:
 * * 1: A topology reference was grabbed successfully
 * * 0: @port is no longer in the topology, no reference was grabbed
 */
static int __must_check
drm_dp_mst_topology_try_get_mstb(struct drm_dp_mst_branch *mstb)
{
        int ret;

        topology_ref_history_lock(mstb->mgr);
        ret = kref_get_unless_zero(&mstb->topology_kref);
        if (ret) {
                DRM_DEBUG("mstb %p (%d)\n",
                          mstb, kref_read(&mstb->topology_kref));
                save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_GET);
        }

        topology_ref_history_unlock(mstb->mgr);

        return ret;
}

/**
 * drm_dp_mst_topology_get_mstb() - Increment the topology refcount of a
 * branch device
 * @mstb: The &struct drm_dp_mst_branch to increment the topology refcount of
 *
 * Increments &drm_dp_mst_branch.topology_refcount without checking whether or
 * not it's already reached 0. This is only valid to use in scenarios where
 * you are already guaranteed to have at least one active topology reference
 * to @mstb. Otherwise, drm_dp_mst_topology_try_get_mstb() must be used.
 *
 * See also:
 * drm_dp_mst_topology_try_get_mstb()
 * drm_dp_mst_topology_put_mstb()
 */
static void drm_dp_mst_topology_get_mstb(struct drm_dp_mst_branch *mstb)
{
        topology_ref_history_lock(mstb->mgr);

        save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_GET);
        WARN_ON(kref_read(&mstb->topology_kref) == 0);
        kref_get(&mstb->topology_kref);
        DRM_DEBUG("mstb %p (%d)\n", mstb, kref_read(&mstb->topology_kref));

        topology_ref_history_unlock(mstb->mgr);
}

/**
 * drm_dp_mst_topology_put_mstb() - release a topology reference to a branch
 * device
 * @mstb: The &struct drm_dp_mst_branch to release the topology reference from
 *
 * Releases a topology reference from @mstb by decrementing
 * &drm_dp_mst_branch.topology_kref.
 *
 * See also:
 * drm_dp_mst_topology_try_get_mstb()
 * drm_dp_mst_topology_get_mstb()
 */
static void
drm_dp_mst_topology_put_mstb(struct drm_dp_mst_branch *mstb)
{
        topology_ref_history_lock(mstb->mgr);

        DRM_DEBUG("mstb %p (%d)\n",
                  mstb, kref_read(&mstb->topology_kref) - 1);
        save_mstb_topology_ref(mstb, DRM_DP_MST_TOPOLOGY_REF_PUT);

        topology_ref_history_unlock(mstb->mgr);
        kref_put(&mstb->topology_kref, drm_dp_destroy_mst_branch_device);
}

static void drm_dp_destroy_port(struct kref *kref)
{
        struct drm_dp_mst_port *port =
                container_of(kref, struct drm_dp_mst_port, topology_kref);
        struct drm_dp_mst_topology_mgr *mgr = port->mgr;

        drm_dp_mst_dump_port_topology_history(port);

        /* There's nothing that needs locking to destroy an input port yet */
        if (port->input) {
                drm_dp_mst_put_port_malloc(port);
                return;
        }

        kfree(port->cached_edid);

        /*
         * we can't destroy the connector here, as we might be holding the
         * mode_config.mutex from an EDID retrieval
         */
        mutex_lock(&mgr->delayed_destroy_lock);
        list_add(&port->next, &mgr->destroy_port_list);
        mutex_unlock(&mgr->delayed_destroy_lock);
        schedule_work(&mgr->delayed_destroy_work);
}

/**
 * drm_dp_mst_topology_try_get_port() - Increment the topology refcount of a
 * port unless it's zero
 * @port: &struct drm_dp_mst_port to increment the topology refcount of
 *
 * Attempts to grab a topology reference to @port, if it hasn't yet been
 * removed from the topology (e.g. &drm_dp_mst_port.topology_kref has reached
 * 0). Holding a topology reference implies that a malloc reference will be
 * held to @port as long as the user holds the topology reference.
 *
 * Care should be taken to ensure that the user has at least one malloc
 * reference to @port. If you already have a topology reference to @port, you
 * should use drm_dp_mst_topology_get_port() instead.
 *
 * See also:
 * drm_dp_mst_topology_get_port()
 * drm_dp_mst_topology_put_port()
 *
 * Returns:
 * * 1: A topology reference was grabbed successfully
 * * 0: @port is no longer in the topology, no reference was grabbed
 */
static int __must_check
drm_dp_mst_topology_try_get_port(struct drm_dp_mst_port *port)
{
        int ret;

        topology_ref_history_lock(port->mgr);
        ret = kref_get_unless_zero(&port->topology_kref);
        if (ret) {
                DRM_DEBUG("port %p (%d)\n",
                          port, kref_read(&port->topology_kref));
                save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_GET);
        }

        topology_ref_history_unlock(port->mgr);
        return ret;
}

/**
 * drm_dp_mst_topology_get_port() - Increment the topology refcount of a port
 * @port: The &struct drm_dp_mst_port to increment the topology refcount of
 *
 * Increments &drm_dp_mst_port.topology_refcount without checking whether or
 * not it's already reached 0. This is only valid to use in scenarios where
 * you are already guaranteed to have at least one active topology reference
 * to @port. Otherwise, drm_dp_mst_topology_try_get_port() must be used.
 *
 * See also:
 * drm_dp_mst_topology_try_get_port()
 * drm_dp_mst_topology_put_port()
 */
static void drm_dp_mst_topology_get_port(struct drm_dp_mst_port *port)
{
        topology_ref_history_lock(port->mgr);

        WARN_ON(kref_read(&port->topology_kref) == 0);
        kref_get(&port->topology_kref);
        DRM_DEBUG("port %p (%d)\n", port, kref_read(&port->topology_kref));
        save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_GET);

        topology_ref_history_unlock(port->mgr);
}

/**
 * drm_dp_mst_topology_put_port() - release a topology reference to a port
 * @port: The &struct drm_dp_mst_port to release the topology reference from
 *
 * Releases a topology reference from @port by decrementing
 * &drm_dp_mst_port.topology_kref.
 *
 * See also:
 * drm_dp_mst_topology_try_get_port()
 * drm_dp_mst_topology_get_port()
 */
static void drm_dp_mst_topology_put_port(struct drm_dp_mst_port *port)
{
        topology_ref_history_lock(port->mgr);

        DRM_DEBUG("port %p (%d)\n",
                  port, kref_read(&port->topology_kref) - 1);
        save_port_topology_ref(port, DRM_DP_MST_TOPOLOGY_REF_PUT);

        topology_ref_history_unlock(port->mgr);
        kref_put(&port->topology_kref, drm_dp_destroy_port);
}

static struct drm_dp_mst_branch *
drm_dp_mst_topology_get_mstb_validated_locked(struct drm_dp_mst_branch *mstb,
                                              struct drm_dp_mst_branch *to_find)
{
        struct drm_dp_mst_port *port;
        struct drm_dp_mst_branch *rmstb;

        if (to_find == mstb)
                return mstb;

        list_for_each_entry(port, &mstb->ports, next) {
                if (port->mstb) {
                        rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
                            port->mstb, to_find);
                        if (rmstb)
                                return rmstb;
                }
        }
        return NULL;
}

static struct drm_dp_mst_branch *
drm_dp_mst_topology_get_mstb_validated(struct drm_dp_mst_topology_mgr *mgr,
                                       struct drm_dp_mst_branch *mstb)
{
        struct drm_dp_mst_branch *rmstb = NULL;

        mutex_lock(&mgr->lock);
        if (mgr->mst_primary) {
                rmstb = drm_dp_mst_topology_get_mstb_validated_locked(
                    mgr->mst_primary, mstb);

                if (rmstb && !drm_dp_mst_topology_try_get_mstb(rmstb))
                        rmstb = NULL;
        }
        mutex_unlock(&mgr->lock);
        return rmstb;
}

static struct drm_dp_mst_port *
drm_dp_mst_topology_get_port_validated_locked(struct drm_dp_mst_branch *mstb,
                                              struct drm_dp_mst_port *to_find)
{
        struct drm_dp_mst_port *port, *mport;

        list_for_each_entry(port, &mstb->ports, next) {
                if (port == to_find)
                        return port;

                if (port->mstb) {
                        mport = drm_dp_mst_topology_get_port_validated_locked(
                            port->mstb, to_find);
                        if (mport)
                                return mport;
                }
        }
        return NULL;
}

static struct drm_dp_mst_port *
drm_dp_mst_topology_get_port_validated(struct drm_dp_mst_topology_mgr *mgr,
                                       struct drm_dp_mst_port *port)
{
        struct drm_dp_mst_port *rport = NULL;

        mutex_lock(&mgr->lock);
        if (mgr->mst_primary) {
                rport = drm_dp_mst_topology_get_port_validated_locked(
                    mgr->mst_primary, port);

                if (rport && !drm_dp_mst_topology_try_get_port(rport))
                        rport = NULL;
        }
        mutex_unlock(&mgr->lock);
        return rport;
}

static struct drm_dp_mst_port *drm_dp_get_port(struct drm_dp_mst_branch *mstb, u8 port_num)
{
        struct drm_dp_mst_port *port;
        int ret;

        list_for_each_entry(port, &mstb->ports, next) {
                if (port->port_num == port_num) {
                        ret = drm_dp_mst_topology_try_get_port(port);
                        return ret ? port : NULL;
                }
        }

        return NULL;
}

/*
 * calculate a new RAD for this MST branch device
 * if parent has an LCT of 2 then it has 1 nibble of RAD,
 * if parent has an LCT of 3 then it has 2 nibbles of RAD,
 */
static u8 drm_dp_calculate_rad(struct drm_dp_mst_port *port,
                                 u8 *rad)
{
        int parent_lct = port->parent->lct;
        int shift = 4;
        int idx = (parent_lct - 1) / 2;
        if (parent_lct > 1) {
                memcpy(rad, port->parent->rad, idx + 1);
                shift = (parent_lct % 2) ? 4 : 0;
        } else
                rad[0] = 0;

        rad[idx] |= port->port_num << shift;
        return parent_lct + 1;
}

static bool drm_dp_mst_is_dp_mst_end_device(u8 pdt, bool mcs)
{
        switch (pdt) {
        case DP_PEER_DEVICE_DP_LEGACY_CONV:
        case DP_PEER_DEVICE_SST_SINK:
                return true;
        case DP_PEER_DEVICE_MST_BRANCHING:
                /* For sst branch device */
                if (!mcs)
                        return true;

                return false;
        }
        return true;
}

static int
drm_dp_port_set_pdt(struct drm_dp_mst_port *port, u8 new_pdt,
                    bool new_mcs)
{
        struct drm_dp_mst_topology_mgr *mgr = port->mgr;
        struct drm_dp_mst_branch *mstb;
        u8 rad[8], lct;
        int ret = 0;

        if (port->pdt == new_pdt && port->mcs == new_mcs)
                return 0;

        /* Teardown the old pdt, if there is one */
        if (port->pdt != DP_PEER_DEVICE_NONE) {
                if (drm_dp_mst_is_dp_mst_end_device(port->pdt, port->mcs)) {
                        /*
                         * If the new PDT would also have an i2c bus,
                         * don't bother with reregistering it
                         */
                        if (new_pdt != DP_PEER_DEVICE_NONE &&
                            drm_dp_mst_is_dp_mst_end_device(new_pdt, new_mcs)) {
                                port->pdt = new_pdt;
                                port->mcs = new_mcs;
                                return 0;
                        }

                        /* remove i2c over sideband */
                        drm_dp_mst_unregister_i2c_bus(&port->aux);
                } else {
                        mutex_lock(&mgr->lock);
                        drm_dp_mst_topology_put_mstb(port->mstb);
                        port->mstb = NULL;
                        mutex_unlock(&mgr->lock);
                }
        }

        port->pdt = new_pdt;
        port->mcs = new_mcs;

        if (port->pdt != DP_PEER_DEVICE_NONE) {
                if (drm_dp_mst_is_dp_mst_end_device(port->pdt, port->mcs)) {
                        /* add i2c over sideband */
                        ret = drm_dp_mst_register_i2c_bus(&port->aux);
                } else {
                        lct = drm_dp_calculate_rad(port, rad);
                        mstb = drm_dp_add_mst_branch_device(lct, rad);
                        if (!mstb) {
                                ret = -ENOMEM;
                                DRM_ERROR("Failed to create MSTB for port %p",
                                          port);
                                goto out;
                        }

                        mutex_lock(&mgr->lock);
                        port->mstb = mstb;
                        mstb->mgr = port->mgr;
                        mstb->port_parent = port;

                        /*
                         * Make sure this port's memory allocation stays
                         * around until its child MSTB releases it
                         */
                        drm_dp_mst_get_port_malloc(port);
                        mutex_unlock(&mgr->lock);

                        /* And make sure we send a link address for this */

                        ret = 1;
                }
        }

out:
        if (ret < 0)
                port->pdt = DP_PEER_DEVICE_NONE;
        return ret;
}

/**
 * drm_dp_mst_dpcd_read() - read a series of bytes from the DPCD via sideband
 * @aux: Fake sideband AUX CH
 * @offset: address of the (first) register to read
 * @buffer: buffer to store the register values
 * @size: number of bytes in @buffer
 *
 * Performs the same functionality for remote devices via
 * sideband messaging as drm_dp_dpcd_read() does for local
 * devices via actual AUX CH.
 *
 * Return: Number of bytes read, or negative error code on failure.
 */
ssize_t drm_dp_mst_dpcd_read(struct drm_dp_aux *aux,
                             unsigned int offset, void *buffer, size_t size)
{
        struct drm_dp_mst_port *port = container_of(aux, struct drm_dp_mst_port,
                                                    aux);

        return drm_dp_send_dpcd_read(port->mgr, port,
                                     offset, size, buffer);
}

/**
 * drm_dp_mst_dpcd_write() - write a series of bytes to the DPCD via sideband
 * @aux: Fake sideband AUX CH
 * @offset: address of the (first) register to write
 * @buffer: buffer containing the values to write
 * @size: number of bytes in @buffer
 *
 * Performs the same functionality for remote devices via
 * sideband messaging as drm_dp_dpcd_write() does for local
 * devices via actual AUX CH.
 *
 * Return: 0 on success, negative error code on failure.
 */
ssize_t drm_dp_mst_dpcd_write(struct drm_dp_aux *aux,
                              unsigned int offset, void *buffer, size_t size)
{
        struct drm_dp_mst_port *port = container_of(aux, struct drm_dp_mst_port,
                                                    aux);

        return drm_dp_send_dpcd_write(port->mgr, port,
                                      offset, size, buffer);
}

static void drm_dp_check_mstb_guid(struct drm_dp_mst_branch *mstb, u8 *guid)
{
        int ret;

        memcpy(mstb->guid, guid, 16);

        if (!drm_dp_validate_guid(mstb->mgr, mstb->guid)) {
                if (mstb->port_parent) {
                        ret = drm_dp_send_dpcd_write(
                                        mstb->mgr,
                                        mstb->port_parent,
                                        DP_GUID,
                                        16,
                                        mstb->guid);
                } else {

                        ret = drm_dp_dpcd_write(
                                        mstb->mgr->aux,
                                        DP_GUID,
                                        mstb->guid,
                                        16);
                }
        }
}

static void build_mst_prop_path(const struct drm_dp_mst_branch *mstb,
                                int pnum,
                                char *proppath,
                                size_t proppath_size)
{
        int i;
        char temp[8];
        snprintf(proppath, proppath_size, "mst:%d", mstb->mgr->conn_base_id);
        for (i = 0; i < (mstb->lct - 1); i++) {
                int shift = (i % 2) ? 0 : 4;
                int port_num = (mstb->rad[i / 2] >> shift) & 0xf;
                snprintf(temp, sizeof(temp), "-%d", port_num);
                strlcat(proppath, temp, proppath_size);
        }
        snprintf(temp, sizeof(temp), "-%d", pnum);
        strlcat(proppath, temp, proppath_size);
}

/**
 * drm_dp_mst_connector_late_register() - Late MST connector registration
 * @connector: The MST connector
 * @port: The MST port for this connector
 *
 * Helper to register the remote aux device for this MST port. Drivers should
 * call this from their mst connector's late_register hook to enable MST aux
 * devices.
 *
 * Return: 0 on success, negative error code on failure.
 */
int drm_dp_mst_connector_late_register(struct drm_connector *connector,
                                       struct drm_dp_mst_port *port)
{
        DRM_DEBUG_KMS("registering %s remote bus for %s\n",
                      port->aux.name, connector->kdev->kobj.name);

        port->aux.dev = connector->kdev;
        return drm_dp_aux_register_devnode(&port->aux);
}
EXPORT_SYMBOL(drm_dp_mst_connector_late_register);

/**
 * drm_dp_mst_connector_early_unregister() - Early MST connector unregistration
 * @connector: The MST connector
 * @port: The MST port for this connector
 *
 * Helper to unregister the remote aux device for this MST port, registered by
 * drm_dp_mst_connector_late_register(). Drivers should call this from their mst
 * connector's early_unregister hook.
 */
void drm_dp_mst_connector_early_unregister(struct drm_connector *connector,
                                           struct drm_dp_mst_port *port)
{
        DRM_DEBUG_KMS("unregistering %s remote bus for %s\n",
                      port->aux.name, connector->kdev->kobj.name);
        drm_dp_aux_unregister_devnode(&port->aux);
}
EXPORT_SYMBOL(drm_dp_mst_connector_early_unregister);

static void
drm_dp_mst_port_add_connector(struct drm_dp_mst_branch *mstb,
                              struct drm_dp_mst_port *port)
{
        struct drm_dp_mst_topology_mgr *mgr = port->mgr;
        char proppath[255];
        int ret;

        build_mst_prop_path(mstb, port->port_num, proppath, sizeof(proppath));
        port->connector = mgr->cbs->add_connector(mgr, port, proppath);
        if (!port->connector) {
                ret = -ENOMEM;
                goto error;
        }

        if (port->pdt != DP_PEER_DEVICE_NONE &&
            drm_dp_mst_is_dp_mst_end_device(port->pdt, port->mcs)) {
                port->cached_edid = drm_get_edid(port->connector,
                                                 &port->aux.ddc);
                drm_connector_set_tile_property(port->connector);
        }

        mgr->cbs->register_connector(port->connector);
        return;

error:
        DRM_ERROR("Failed to create connector for port %p: %d\n", port, ret);
}

/*
 * Drop a topology reference, and unlink the port from the in-memory topology
 * layout
 */
static void
drm_dp_mst_topology_unlink_port(struct drm_dp_mst_topology_mgr *mgr,
                                struct drm_dp_mst_port *port)
{
        mutex_lock(&mgr->lock);
        list_del(&port->next);
        mutex_unlock(&mgr->lock);
        drm_dp_mst_topology_put_port(port);
}

static struct drm_dp_mst_port *
drm_dp_mst_add_port(struct drm_device *dev,
                    struct drm_dp_mst_topology_mgr *mgr,
                    struct drm_dp_mst_branch *mstb, u8 port_number)
{
        struct drm_dp_mst_port *port = kzalloc(sizeof(*port), GFP_KERNEL);

        if (!port)
                return NULL;

        kref_init(&port->topology_kref);
        kref_init(&port->malloc_kref);
        port->parent = mstb;
        port->port_num = port_number;
        port->mgr = mgr;
        port->aux.name = "DPMST";
        port->aux.dev = dev->dev;
        port->aux.is_remote = true;

        /*
         * Make sure the memory allocation for our parent branch stays
         * around until our own memory allocation is released
         */
        drm_dp_mst_get_mstb_malloc(mstb);

        return port;
}

static int
drm_dp_mst_handle_link_address_port(struct drm_dp_mst_branch *mstb,
                                    struct drm_device *dev,
                                    struct drm_dp_link_addr_reply_port *port_msg)
{
        struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
        struct drm_dp_mst_port *port;
        int old_ddps = 0, ret;
        u8 new_pdt = DP_PEER_DEVICE_NONE;
        bool new_mcs = 0;
        bool created = false, send_link_addr = false, changed = false;

        port = drm_dp_get_port(mstb, port_msg->port_number);
        if (!port) {
                port = drm_dp_mst_add_port(dev, mgr, mstb,
                                           port_msg->port_number);
                if (!port)
                        return -ENOMEM;
                created = true;
                changed = true;
        } else if (!port->input && port_msg->input_port && port->connector) {
                /* Since port->connector can't be changed here, we create a
                 * new port if input_port changes from 0 to 1
                 */
                drm_dp_mst_topology_unlink_port(mgr, port);
                drm_dp_mst_topology_put_port(port);
                port = drm_dp_mst_add_port(dev, mgr, mstb,
                                           port_msg->port_number);
                if (!port)
                        return -ENOMEM;
                changed = true;
                created = true;
        } else if (port->input && !port_msg->input_port) {
                changed = true;
        } else if (port->connector) {
                /* We're updating a port that's exposed to userspace, so do it
                 * under lock
                 */
                drm_modeset_lock(&mgr->base.lock, NULL);

                old_ddps = port->ddps;
                changed = port->ddps != port_msg->ddps ||
                        (port->ddps &&
                         (port->ldps != port_msg->legacy_device_plug_status ||
                          port->dpcd_rev != port_msg->dpcd_revision ||
                          port->mcs != port_msg->mcs ||
                          port->pdt != port_msg->peer_device_type ||
                          port->num_sdp_stream_sinks !=
                          port_msg->num_sdp_stream_sinks));
        }

        port->input = port_msg->input_port;
        if (!port->input)
                new_pdt = port_msg->peer_device_type;
        new_mcs = port_msg->mcs;
        port->ddps = port_msg->ddps;
        port->ldps = port_msg->legacy_device_plug_status;
        port->dpcd_rev = port_msg->dpcd_revision;
        port->num_sdp_streams = port_msg->num_sdp_streams;
        port->num_sdp_stream_sinks = port_msg->num_sdp_stream_sinks;

        /* manage mstb port lists with mgr lock - take a reference
           for this list */
        if (created) {
                mutex_lock(&mgr->lock);
                drm_dp_mst_topology_get_port(port);
                list_add(&port->next, &mstb->ports);
                mutex_unlock(&mgr->lock);
        }

        if (old_ddps != port->ddps) {
                if (port->ddps) {
                        if (!port->input) {
                                drm_dp_send_enum_path_resources(mgr, mstb,
                                                                port);
                        }
                } else {
                        port->available_pbn = 0;
                }
        }

        ret = drm_dp_port_set_pdt(port, new_pdt, new_mcs);
        if (ret == 1) {
                send_link_addr = true;
        } else if (ret < 0) {
                DRM_ERROR("Failed to change PDT on port %p: %d\n",
                          port, ret);
                goto fail;
        }

        /*
         * If this port wasn't just created, then we're reprobing because
         * we're coming out of suspend. In this case, always resend the link
         * address if there's an MSTB on this port
         */
        if (!created && port->pdt == DP_PEER_DEVICE_MST_BRANCHING &&
            port->mcs)
                send_link_addr = true;

        if (port->connector)
                drm_modeset_unlock(&mgr->base.lock);
        else if (!port->input)
                drm_dp_mst_port_add_connector(mstb, port);

        if (send_link_addr && port->mstb) {
                ret = drm_dp_send_link_address(mgr, port->mstb);
                if (ret == 1) /* MSTB below us changed */
                        changed = true;
                else if (ret < 0)
                        goto fail_put;
        }

        /* put reference to this port */
        drm_dp_mst_topology_put_port(port);
        return changed;

fail:
        drm_dp_mst_topology_unlink_port(mgr, port);
        if (port->connector)
                drm_modeset_unlock(&mgr->base.lock);
fail_put:
        drm_dp_mst_topology_put_port(port);
        return ret;
}

static void
drm_dp_mst_handle_conn_stat(struct drm_dp_mst_branch *mstb,
                            struct drm_dp_connection_status_notify *conn_stat)
{
        struct drm_dp_mst_topology_mgr *mgr = mstb->mgr;
        struct drm_dp_mst_port *port;
        int old_ddps, old_input, ret, i;
        u8 new_pdt;
        bool new_mcs;
        bool dowork = false, create_connector = false;

        port = drm_dp_get_port(mstb, conn_stat->port_number);
        if (!port)
                return;

        if (port->connector) {
                if (!port->input && conn_stat->input_port) {
                        /*
                         * We can't remove a connector from an already exposed
                         * port, so just throw the port out and make sure we
                         * reprobe the link address of it's parent MSTB
                         */
                        drm_dp_mst_topology_unlink_port(mgr, port);
                        mstb->link_address_sent = false;
                        dowork = true;
                        goto out;
                }

                /* Locking is only needed if the port's exposed to userspace */
                drm_modeset_lock(&mgr->base.lock, NULL);
        } else if (port->input && !conn_stat->input_port) {
                create_connector = true;
                /* Reprobe link address so we get num_sdp_streams */
                mstb->link_address_sent = false;
                dowork = true;
        }

        old_ddps = port->ddps;
        old_input = port->input;
        port->input = conn_stat->input_port;
        port->ldps = conn_stat->legacy_device_plug_status;
        port->ddps = conn_stat->displayport_device_plug_status;

        if (old_ddps != port->ddps) {
                if (port->ddps) {
                        dowork = true;
                } else {
                        port->available_pbn = 0;
                }
        }

        new_pdt = port->input ? DP_PEER_DEVICE_NONE : conn_stat->peer_device_type;
        new_mcs = conn_stat->message_capability_status;
        ret = drm_dp_port_set_pdt(port, new_pdt, new_mcs);
        if (ret == 1) {
                dowork = true;
        } else if (ret < 0) {
                DRM_ERROR("Failed to change PDT for port %p: %d\n",
                          port, ret);
                dowork = false;
        }

        if (!old_input && old_ddps != port->ddps && !port->ddps) {
                for (i = 0; i < mgr->max_payloads; i++) {
                        struct drm_dp_vcpi *vcpi = mgr->proposed_vcpis[i];
                        struct drm_dp_mst_port *port_validated;

                        if (!vcpi)
                                continue;

                        port_validated =
                                container_of(vcpi, struct drm_dp_mst_port, vcpi);
                        port_validated =
                                drm_dp_mst_topology_get_port_validated(mgr, port_validated);
                        if (!port_validated) {
                                mutex_lock(&mgr->payload_lock);
                                vcpi->num_slots = 0;
                                mutex_unlock(&mgr->payload_lock);
                        } else {
                                drm_dp_mst_topology_put_port(port_validated);
                        }
                }
        }

        if (port->connector)
                drm_modeset_unlock(&mgr->base.lock);
        else if (create_connector)
                drm_dp_mst_port_add_connector(mstb, port);

out:
        drm_dp_mst_topology_put_port(port);
        if (dowork)
                queue_work(system_long_wq, &mstb->mgr->work);
}

static struct drm_dp_mst_branch *drm_dp_get_mst_branch_device(struct drm_dp_mst_topology_mgr *mgr,
                                                               u8 lct, u8 *rad)
{
        struct drm_dp_mst_branch *mstb;
        struct drm_dp_mst_port *port;
        int i, ret;
        /* find the port by iterating down */

        mutex_lock(&mgr->lock);
        mstb = mgr->mst_primary;

        if (!mstb)
                goto out;

        for (i = 0; i < lct - 1; i++) {
                int shift = (i % 2) ? 0 : 4;
                int port_num = (rad[i / 2] >> shift) & 0xf;

                list_for_each_entry(port, &mstb->ports, next) {
                        if (port->port_num == port_num) {
                                mstb = port->mstb;
                                if (!mstb) {
                                        DRM_ERROR("failed to lookup MSTB with lct %d, rad %02x\n", lct, rad[0]);
                                        goto out;
                                }

                                break;
                        }
                }
        }
        ret = drm_dp_mst_topology_try_get_mstb(mstb);
        if (!ret)
                mstb = NULL;
out:
        mutex_unlock(&mgr->lock);
        return mstb;
}

static struct drm_dp_mst_branch *get_mst_branch_device_by_guid_helper(
        struct drm_dp_mst_branch *mstb,
        const uint8_t *guid)
{
        struct drm_dp_mst_branch *found_mstb;
        struct drm_dp_mst_port *port;

        if (memcmp(mstb->guid, guid, 16) == 0)
                return mstb;


        list_for_each_entry(port, &mstb->ports, next) {
                if (!port->mstb)
                        continue;

                found_mstb = get_mst_branch_device_by_guid_helper(port->mstb, guid);

                if (found_mstb)
                        return found_mstb;
        }

        return NULL;
}

static struct drm_dp_mst_branch *
drm_dp_get_mst_branch_device_by_guid(struct drm_dp_mst_topology_mgr *mgr,
                                     const uint8_t *guid)
{
        struct drm_dp_mst_branch *mstb;
        int ret;

        /* find the port by iterating down */
        mutex_lock(&mgr->lock);

        mstb = get_mst_branch_device_by_guid_helper(mgr->mst_primary, guid);
        if (mstb) {
                ret = drm_dp_mst_topology_try_get_mstb(mstb);
                if (!ret)
                        mstb = NULL;
        }

        mutex_unlock(&mgr->lock);
        return mstb;
}

static int drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
                                               struct drm_dp_mst_branch *mstb)
{
        struct drm_dp_mst_port *port;
        int ret;
        bool changed = false;

        if (!mstb->link_address_sent) {
                ret = drm_dp_send_link_address(mgr, mstb);
                if (ret == 1)
                        changed = true;
                else if (ret < 0)
                        return ret;
        }

        list_for_each_entry(port, &mstb->ports, next) {
                struct drm_dp_mst_branch *mstb_child = NULL;

                if (port->input || !port->ddps)
                        continue;

                if (!port->available_pbn) {
                        drm_modeset_lock(&mgr->base.lock, NULL);
                        drm_dp_send_enum_path_resources(mgr, mstb, port);
                        drm_modeset_unlock(&mgr->base.lock);
                        changed = true;
                }

                if (port->mstb)
                        mstb_child = drm_dp_mst_topology_get_mstb_validated(
                            mgr, port->mstb);

                if (mstb_child) {
                        ret = drm_dp_check_and_send_link_address(mgr,
                                                                 mstb_child);
                        drm_dp_mst_topology_put_mstb(mstb_child);
                        if (ret == 1)
                                changed = true;
                        else if (ret < 0)
                                return ret;
                }
        }

        return changed;
}

static void drm_dp_mst_link_probe_work(struct work_struct *work)
{
        struct drm_dp_mst_topology_mgr *mgr =
                container_of(work, struct drm_dp_mst_topology_mgr, work);
        struct drm_device *dev = mgr->dev;
        struct drm_dp_mst_branch *mstb;
        int ret;

        mutex_lock(&mgr->probe_lock);

        mutex_lock(&mgr->lock);
        mstb = mgr->mst_primary;
        if (mstb) {
                ret = drm_dp_mst_topology_try_get_mstb(mstb);
                if (!ret)
                        mstb = NULL;
        }
        mutex_unlock(&mgr->lock);
        if (!mstb) {
                mutex_unlock(&mgr->probe_lock);
                return;
        }

        ret = drm_dp_check_and_send_link_address(mgr, mstb);
        drm_dp_mst_topology_put_mstb(mstb);

        mutex_unlock(&mgr->probe_lock);
        if (ret)
                drm_kms_helper_hotplug_event(dev);
}

static bool drm_dp_validate_guid(struct drm_dp_mst_topology_mgr *mgr,
                                 u8 *guid)
{
        u64 salt;

        if (memchr_inv(guid, 0, 16))
                return true;

        salt = get_jiffies_64();

        memcpy(&guid[0], &salt, sizeof(u64));
        memcpy(&guid[8], &salt, sizeof(u64));

        return false;
}

static int build_dpcd_read(struct drm_dp_sideband_msg_tx *msg, u8 port_num, u32 offset, u8 num_bytes)
{
        struct drm_dp_sideband_msg_req_body req;

        req.req_type = DP_REMOTE_DPCD_READ;
        req.u.dpcd_read.port_number = port_num;
        req.u.dpcd_read.dpcd_address = offset;
        req.u.dpcd_read.num_bytes = num_bytes;
        drm_dp_encode_sideband_req(&req, msg);

        return 0;
}

static int drm_dp_send_sideband_msg(struct drm_dp_mst_topology_mgr *mgr,
                                    bool up, u8 *msg, int len)
{
        int ret;
        int regbase = up ? DP_SIDEBAND_MSG_UP_REP_BASE : DP_SIDEBAND_MSG_DOWN_REQ_BASE;
        int tosend, total, offset;
        int retries = 0;

retry:
        total = len;
        offset = 0;
        do {
                tosend = min3(mgr->max_dpcd_transaction_bytes, 16, total);

                ret = drm_dp_dpcd_write(mgr->aux, regbase + offset,
                                        &msg[offset],
                                        tosend);
                if (ret != tosend) {
                        if (ret == -EIO && retries < 5) {
                                retries++;
                                goto retry;
                        }
                        DRM_DEBUG_KMS("failed to dpcd write %d %d\n", tosend, ret);

                        return -EIO;
                }
                offset += tosend;
                total -= tosend;
        } while (total > 0);
        return 0;
}

static int set_hdr_from_dst_qlock(struct drm_dp_sideband_msg_hdr *hdr,
                                  struct drm_dp_sideband_msg_tx *txmsg)
{
        struct drm_dp_mst_branch *mstb = txmsg->dst;
        u8 req_type;

        /* both msg slots are full */
        if (txmsg->seqno == -1) {
                if (mstb->tx_slots[0] && mstb->tx_slots[1]) {
                        DRM_DEBUG_KMS("%s: failed to find slot\n", __func__);
                        return -EAGAIN;
                }
                if (mstb->tx_slots[0] == NULL && mstb->tx_slots[1] == NULL) {
                        txmsg->seqno = mstb->last_seqno;
                        mstb->last_seqno ^= 1;
                } else if (mstb->tx_slots[0] == NULL)
                        txmsg->seqno = 0;
                else
                        txmsg->seqno = 1;
                mstb->tx_slots[txmsg->seqno] = txmsg;
        }

        req_type = txmsg->msg[0] & 0x7f;
        if (req_type == DP_CONNECTION_STATUS_NOTIFY ||
                req_type == DP_RESOURCE_STATUS_NOTIFY)
                hdr->broadcast = 1;
        else
                hdr->broadcast = 0;
        hdr->path_msg = txmsg->path_msg;
        hdr->lct = mstb->lct;
        hdr->lcr = mstb->lct - 1;
        if (mstb->lct > 1)
                memcpy(hdr->rad, mstb->rad, mstb->lct / 2);
        hdr->seqno = txmsg->seqno;
        return 0;
}
/*
 * process a single block of the next message in the sideband queue
 */
static int process_single_tx_qlock(struct drm_dp_mst_topology_mgr *mgr,
                                   struct drm_dp_sideband_msg_tx *txmsg,
                                   bool up)
{
        u8 chunk[48];
        struct drm_dp_sideband_msg_hdr hdr;
        int len, space, idx, tosend;
        int ret;

        memset(&hdr, 0, sizeof(struct drm_dp_sideband_msg_hdr));

        if (txmsg->state == DRM_DP_SIDEBAND_TX_QUEUED) {
                txmsg->seqno = -1;
                txmsg->state = DRM_DP_SIDEBAND_TX_START_SEND;
        }

        /* make hdr from dst mst - for replies use seqno
           otherwise assign one */
        ret = set_hdr_from_dst_qlock(&hdr, txmsg);
        if (ret < 0)
                return ret;

        /* amount left to send in this message */
        len = txmsg->cur_len - txmsg->cur_offset;

        /* 48 - sideband msg size - 1 byte for data CRC, x header bytes */
        space = 48 - 1 - drm_dp_calc_sb_hdr_size(&hdr);

        tosend = min(len, space);
        if (len == txmsg->cur_len)
                hdr.somt = 1;
        if (space >= len)
                hdr.eomt = 1;


        hdr.msg_len = tosend + 1;
        drm_dp_encode_sideband_msg_hdr(&hdr, chunk, &idx);
        memcpy(&chunk[idx], &txmsg->msg[txmsg->cur_offset], tosend);
        /* add crc at end */
        drm_dp_crc_sideband_chunk_req(&chunk[idx], tosend);
        idx += tosend + 1;

        ret = drm_dp_send_sideband_msg(mgr, up, chunk, idx);
        if (unlikely(ret) && drm_debug_enabled(DRM_UT_DP)) {
                struct drm_printer p = drm_debug_printer(DBG_PREFIX);

                drm_printf(&p, "sideband msg failed to send\n");
                drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
                return ret;
        }

        txmsg->cur_offset += tosend;
        if (txmsg->cur_offset == txmsg->cur_len) {
                txmsg->state = DRM_DP_SIDEBAND_TX_SENT;
                return 1;
        }
        return 0;
}

static void process_single_down_tx_qlock(struct drm_dp_mst_topology_mgr *mgr)
{
        struct drm_dp_sideband_msg_tx *txmsg;
        int ret;

        WARN_ON(!mutex_is_locked(&mgr->qlock));

        /* construct a chunk from the first msg in the tx_msg queue */
        if (list_empty(&mgr->tx_msg_downq))
                return;

        txmsg = list_first_entry(&mgr->tx_msg_downq, struct drm_dp_sideband_msg_tx, next);
        ret = process_single_tx_qlock(mgr, txmsg, false);
        if (ret == 1) {
                /* txmsg is sent it should be in the slots now */
                mgr->is_waiting_for_dwn_reply = true;
                list_del(&txmsg->next);
        } else if (ret) {
                DRM_DEBUG_KMS("failed to send msg in q %d\n", ret);
                mgr->is_waiting_for_dwn_reply = false;
                list_del(&txmsg->next);
                if (txmsg->seqno != -1)
                        txmsg->dst->tx_slots[txmsg->seqno] = NULL;
                txmsg->state = DRM_DP_SIDEBAND_TX_TIMEOUT;
                wake_up_all(&mgr->tx_waitq);
        }
}

/* called holding qlock */
static void process_single_up_tx_qlock(struct drm_dp_mst_topology_mgr *mgr,
                                       struct drm_dp_sideband_msg_tx *txmsg)
{
        int ret;

        /* construct a chunk from the first msg in the tx_msg queue */
        ret = process_single_tx_qlock(mgr, txmsg, true);

        if (ret != 1)
                DRM_DEBUG_KMS("failed to send msg in q %d\n", ret);

        if (txmsg->seqno != -1) {
                WARN_ON((unsigned int)txmsg->seqno >
                        ARRAY_SIZE(txmsg->dst->tx_slots));
                txmsg->dst->tx_slots[txmsg->seqno] = NULL;
        }
}

static void drm_dp_queue_down_tx(struct drm_dp_mst_topology_mgr *mgr,
                                 struct drm_dp_sideband_msg_tx *txmsg)
{
        mutex_lock(&mgr->qlock);
        list_add_tail(&txmsg->next, &mgr->tx_msg_downq);

        if (drm_debug_enabled(DRM_UT_DP)) {
                struct drm_printer p = drm_debug_printer(DBG_PREFIX);

                drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
        }

        if (list_is_singular(&mgr->tx_msg_downq) &&
            !mgr->is_waiting_for_dwn_reply)
                process_single_down_tx_qlock(mgr);
        mutex_unlock(&mgr->qlock);
}

static void
drm_dp_dump_link_address(struct drm_dp_link_address_ack_reply *reply)
{
        struct drm_dp_link_addr_reply_port *port_reply;
        int i;

        for (i = 0; i < reply->nports; i++) {
                port_reply = &reply->ports[i];
                DRM_DEBUG_KMS("port %d: input %d, pdt: %d, pn: %d, dpcd_rev: %02x, mcs: %d, ddps: %d, ldps %d, sdp %d/%d\n",
                              i,
                              port_reply->input_port,
                              port_reply->peer_device_type,
                              port_reply->port_number,
                              port_reply->dpcd_revision,
                              port_reply->mcs,
                              port_reply->ddps,
                              port_reply->legacy_device_plug_status,
                              port_reply->num_sdp_streams,
                              port_reply->num_sdp_stream_sinks);
        }
}

static int drm_dp_send_link_address(struct drm_dp_mst_topology_mgr *mgr,
                                     struct drm_dp_mst_branch *mstb)
{
        struct drm_dp_sideband_msg_tx *txmsg;
        struct drm_dp_link_address_ack_reply *reply;
        struct drm_dp_mst_port *port, *tmp;
        int i, len, ret, port_mask = 0;
        bool changed = false;

        txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
        if (!txmsg)
                return -ENOMEM;

        txmsg->dst = mstb;
        len = build_link_address(txmsg);

        mstb->link_address_sent = true;
        drm_dp_queue_down_tx(mgr, txmsg);

        /* FIXME: Actually do some real error handling here */
        ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
        if (ret <= 0) {
                DRM_ERROR("Sending link address failed with %d\n", ret);
                goto out;
        }
        if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
                DRM_ERROR("link address NAK received\n");
                ret = -EIO;
                goto out;
        }

        reply = &txmsg->reply.u.link_addr;
        DRM_DEBUG_KMS("link address reply: %d\n", reply->nports);
        drm_dp_dump_link_address(reply);

        drm_dp_check_mstb_guid(mstb, reply->guid);

        for (i = 0; i < reply->nports; i++) {
                port_mask |= BIT(reply->ports[i].port_number);
                ret = drm_dp_mst_handle_link_address_port(mstb, mgr->dev,
                                                          &reply->ports[i]);
                if (ret == 1)
                        changed = true;
                else if (ret < 0)
                        goto out;
        }

        /* Prune any ports that are currently a part of mstb in our in-memory
         * topology, but were not seen in this link address. Usually this
         * means that they were removed while the topology was out of sync,
         * e.g. during suspend/resume
         */
        mutex_lock(&mgr->lock);
        list_for_each_entry_safe(port, tmp, &mstb->ports, next) {
                if (port_mask & BIT(port->port_num))
                        continue;

                DRM_DEBUG_KMS("port %d was not in link address, removing\n",
                              port->port_num);
                list_del(&port->next);
                drm_dp_mst_topology_put_port(port);
                changed = true;
        }
        mutex_unlock(&mgr->lock);

out:
        if (ret <= 0)
                mstb->link_address_sent = false;
        kfree(txmsg);
        return ret < 0 ? ret : changed;
}

static int
drm_dp_send_enum_path_resources(struct drm_dp_mst_topology_mgr *mgr,
                                struct drm_dp_mst_branch *mstb,
                                struct drm_dp_mst_port *port)
{
        struct drm_dp_enum_path_resources_ack_reply *path_res;
        struct drm_dp_sideband_msg_tx *txmsg;
        int len;
        int ret;

        txmsg = kzalloc(sizeof(*txmsg), GFP_KERNEL);
        if (!txmsg)
                return -ENOMEM;

        txmsg->dst = mstb;
        len = build_enum_path_resources(txmsg, port->port_num);

        drm_dp_queue_down_tx(mgr, txmsg);

        ret = drm_dp_mst_wait_tx_reply(mstb, txmsg);
        if (ret > 0) {
                path_res = &txmsg->reply.u.path_resources;

                if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
                        DRM_DEBUG_KMS("enum path resources nak received\n");
                } else {
                        if (port->port_num != path_res->port_number)
                                DRM_ERROR("got incorrect port in response\n");

                        DRM_DEBUG_KMS("enum path resources %d: %d %d\n",
                                      path_res->port_number,
                                      path_res->full_payload_bw_number,
                                      path_res->avail_payload_bw_number);
                        port->available_pbn =
                                path_res->avail_payload_bw_number;
                }
        }

        kfree(txmsg);
        return 0;
}

static struct drm_dp_mst_port *drm_dp_get_last_connected_port_to_mstb(struct drm_dp_mst_branch *mstb)
{
        if (!mstb->port_parent)
                return NULL;

        if (mstb->port_parent->mstb != mstb)
                return mstb->port_parent;

        return drm_dp_get_last_connected_port_to_mstb(mstb->port_parent->parent);
}

/*
 * Searches upwards in the topology starting from mstb to try to find the
 * closest available parent of mstb that's still connected to the rest of the
 * topology. This can be used in order to perform operations like releasing
 * payloads, where the branch device which owned the payload may no longer be
 * around and thus would require that the payload on the last living relative
 * be freed instead.
 */
static struct drm_dp_mst_branch *
drm_dp_get_last_connected_port_and_mstb(struct drm_dp_mst_topology_mgr *mgr,
                                        struct drm_dp_mst_branch *mstb,
                                        int *port_num)
{
        struct drm_dp_mst_branch *rmstb = NULL;
        struct drm_dp_mst_port *found_port;

        mutex_lock(&mgr->lock);
        if (!mgr->mst_primary)
                goto out;

        do {
                found_port = drm_dp_get_last_connected_port_to_mstb(mstb);
                if (!found_port)
                        break;

                if (drm_dp_mst_topology_try_get_mstb(found_port->parent)) {
                        rmstb = found_port->parent;
                        *port_num = found_port->port_num;
                } else {
                        /* Search again, starting from this parent */
                        mstb = found_port->parent;
                }
        } while (!rmstb);
out:
        mutex_unlock(&mgr->lock);
        return rmstb;
}

static int drm_dp_payload_send_msg(struct drm_dp_mst_topology_mgr *mgr,