// SPDX-License-Identifier: GPL-2.0
/*
 * DisplayPort CEC-Tunneling-over-AUX support
 *
 * Copyright 2018 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <drm/drm_dp_helper.h>
#include <media/cec.h>

/*
 * Unfortunately it turns out that we have a chicken-and-egg situation
 * here. Quite a few active (mini-)DP-to-HDMI or USB-C-to-HDMI adapters
 * have a converter chip that supports CEC-Tunneling-over-AUX (usually the
 * Parade PS176), but they do not wire up the CEC pin, thus making CEC
 * useless. Note that MegaChips 2900-based adapters appear to have good
 * support for CEC tunneling. Those adapters that I have tested using
 * this chipset all have the CEC line connected.
 *
 * Sadly there is no way for this driver to know this. What happens is
 * that a /dev/cecX device is created that is isolated and unable to see
 * any of the other CEC devices. Quite literally the CEC wire is cut
 * (or in this case, never connected in the first place).
 *
 * The reason so few adapters support this is that this tunneling protocol
 * was never supported by any OS. So there was no easy way of testing it,
 * and no incentive to correctly wire up the CEC pin.
 *
 * Hopefully by creating this driver it will be easier for vendors to
 * finally fix their adapters and test the CEC functionality.
 *
 * I keep a list of known working adapters here:
 *
 * https://hverkuil.home.xs4all.nl/cec-status.txt
 *
 * Please mail me (hverkuil@xs4all.nl) if you find an adapter that works
 * and is not yet listed there.
 *
 * Note that the current implementation does not support CEC over an MST hub.
 * As far as I can see there is no mechanism defined in the DisplayPort
 * standard to transport CEC interrupts over an MST device. It might be
 * possible to do this through polling, but I have not been able to get that
 * to work.
 */

/**
 * DOC: dp cec helpers
 *
 * These functions take care of supporting the CEC-Tunneling-over-AUX
 * feature of DisplayPort-to-HDMI adapters.
 */

/*
 * When the EDID is unset because the HPD went low, then the CEC DPCD registers
 * typically can no longer be read (true for a DP-to-HDMI adapter since it is
 * powered by the HPD). However, some displays toggle the HPD off and on for a
 * short period for one reason or another, and that would cause the CEC adapter
 * to be removed and added again, even though nothing else changed.
 *
 * This module parameter sets a delay in seconds before the CEC adapter is
 * actually unregistered. Only if the HPD does not return within that time will
 * the CEC adapter be unregistered.
 *
 * If it is set to a value >= NEVER_UNREG_DELAY, then the CEC adapter will never
 * be unregistered for as long as the connector remains registered.
 *
 * If it is set to 0, then the CEC adapter will be unregistered immediately as
 * soon as the HPD disappears.
 *
 * The default is one second to prevent short HPD glitches from unregistering
 * the CEC adapter.
 *
 * Note that for integrated HDMI branch devices that support CEC the DPCD
 * registers remain available even if the HPD goes low since it is not powered
 * by the HPD. In that case the CEC adapter will never be unregistered during
 * the life time of the connector. At least, this is the theory since I do not
 * have hardware with an integrated HDMI branch device that supports CEC.
 */
#define NEVER_UNREG_DELAY 1000
static unsigned int drm_dp_cec_unregister_delay = 1;
module_param(drm_dp_cec_unregister_delay, uint, 0600);
MODULE_PARM_DESC(drm_dp_cec_unregister_delay,
                 "CEC unregister delay in seconds, 0: no delay, >= 1000: never unregister");

static int drm_dp_cec_adap_enable(struct cec_adapter *adap, bool enable)
{
        struct drm_dp_aux *aux = cec_get_drvdata(adap);
        u32 val = enable ? DP_CEC_TUNNELING_ENABLE : 0;
        ssize_t err = 0;

        err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
        return (enable && err < 0) ? err : 0;
}

static int drm_dp_cec_adap_log_addr(struct cec_adapter *adap, u8 addr)
{
        struct drm_dp_aux *aux = cec_get_drvdata(adap);
        /* Bit 15 (logical address 15) should always be set */
        u16 la_mask = 1 << CEC_LOG_ADDR_BROADCAST;
        u8 mask[2];
        ssize_t err;

        if (addr != CEC_LOG_ADDR_INVALID)
                la_mask |= adap->log_addrs.log_addr_mask | (1 << addr);
        mask[0] = la_mask & 0xff;
        mask[1] = la_mask >> 8;
        err = drm_dp_dpcd_write(aux, DP_CEC_LOGICAL_ADDRESS_MASK, mask, 2);
        return (addr != CEC_LOG_ADDR_INVALID && err < 0) ? err : 0;
}

static int drm_dp_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
                                    u32 signal_free_time, struct cec_msg *msg)
{
        struct drm_dp_aux *aux = cec_get_drvdata(adap);
        unsigned int retries = min(5, attempts - 1);
        ssize_t err;

        err = drm_dp_dpcd_write(aux, DP_CEC_TX_MESSAGE_BUFFER,
                                msg->msg, msg->len);
        if (err < 0)
                return err;

        err = drm_dp_dpcd_writeb(aux, DP_CEC_TX_MESSAGE_INFO,
                                 (msg->len - 1) | (retries << 4) |
                                 DP_CEC_TX_MESSAGE_SEND);
        return err < 0 ? err : 0;
}

static int drm_dp_cec_adap_monitor_all_enable(struct cec_adapter *adap,
                                              bool enable)
{
        struct drm_dp_aux *aux = cec_get_drvdata(adap);
        ssize_t err;
        u8 val;

        if (!(adap->capabilities & CEC_CAP_MONITOR_ALL))
                return 0;

        err = drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CONTROL, &val);
        if (err >= 0) {
                if (enable)
                        val |= DP_CEC_SNOOPING_ENABLE;
                else
                        val &= ~DP_CEC_SNOOPING_ENABLE;
                err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
        }
        return (enable && err < 0) ? err : 0;
}

static void drm_dp_cec_adap_status(struct cec_adapter *adap,
                                   struct seq_file *file)
{
        struct drm_dp_aux *aux = cec_get_drvdata(adap);
        struct drm_dp_desc desc;
        struct drm_dp_dpcd_ident *id = &desc.ident;

        if (drm_dp_read_desc(aux, &desc, true))
                return;
        seq_printf(file, "OUI: %*phD\n",
                   (int)sizeof(id->oui), id->oui);
        seq_printf(file, "ID: %*pE\n",
                   (int)strnlen(id->device_id, sizeof(id->device_id)),
                   id->device_id);
        seq_printf(file, "HW Rev: %d.%d\n", id->hw_rev >> 4, id->hw_rev & 0xf);
        /*
         * Show this both in decimal and hex: at least one vendor
         * always reports this in hex.
         */
        seq_printf(file, "FW/SW Rev: %d.%d (0x%02x.0x%02x)\n",
                   id->sw_major_rev, id->sw_minor_rev,
                   id->sw_major_rev, id->sw_minor_rev);
}

static const struct cec_adap_ops drm_dp_cec_adap_ops = {
        .adap_enable = drm_dp_cec_adap_enable,
        .adap_log_addr = drm_dp_cec_adap_log_addr,
        .adap_transmit = drm_dp_cec_adap_transmit,
        .adap_monitor_all_enable = drm_dp_cec_adap_monitor_all_enable,
        .adap_status = drm_dp_cec_adap_status,
};

static int drm_dp_cec_received(struct drm_dp_aux *aux)
{
        struct cec_adapter *adap = aux->cec.adap;
        struct cec_msg msg;
        u8 rx_msg_info;
        ssize_t err;

        err = drm_dp_dpcd_readb(aux, DP_CEC_RX_MESSAGE_INFO, &rx_msg_info);
        if (err < 0)
                return err;

        if (!(rx_msg_info & DP_CEC_RX_MESSAGE_ENDED))
                return 0;

        msg.len = (rx_msg_info & DP_CEC_RX_MESSAGE_LEN_MASK) + 1;
        err = drm_dp_dpcd_read(aux, DP_CEC_RX_MESSAGE_BUFFER, msg.msg, msg.len);
        if (err < 0)
                return err;

        cec_received_msg(adap, &msg);
        return 0;
}

static void drm_dp_cec_handle_irq(struct drm_dp_aux *aux)
{
        struct cec_adapter *adap = aux->cec.adap;
        u8 flags;

        if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, &flags) < 0)
                return;

        if (flags & DP_CEC_RX_MESSAGE_INFO_VALID)
                drm_dp_cec_received(aux);

        if (flags & DP_CEC_TX_MESSAGE_SENT)
                cec_transmit_attempt_done(adap, CEC_TX_STATUS_OK);
        else if (flags & DP_CEC_TX_LINE_ERROR)
                cec_transmit_attempt_done(adap, CEC_TX_STATUS_ERROR |
                                                CEC_TX_STATUS_MAX_RETRIES);
        else if (flags &
                 (DP_CEC_TX_ADDRESS_NACK_ERROR | DP_CEC_TX_DATA_NACK_ERROR))
                cec_transmit_attempt_done(adap, CEC_TX_STATUS_NACK |
                                                CEC_TX_STATUS_MAX_RETRIES);
        drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, flags);
}

/**
 * drm_dp_cec_irq() - handle CEC interrupt, if any
 * @aux: DisplayPort AUX channel
 *
 * Should be called when handling an IRQ_HPD request. If CEC-tunneling-over-AUX
 * is present, then it will check for a CEC_IRQ and handle it accordingly.
 */
void drm_dp_cec_irq(struct drm_dp_aux *aux)
{
        u8 cec_irq;
        int ret;

        /* No transfer function was set, so not a DP connector */
        if (!aux->transfer)
                return;

        mutex_lock(&aux->cec.lock);
        if (!aux->cec.adap)
                goto unlock;

        ret = drm_dp_dpcd_readb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
                                &cec_irq);
        if (ret < 0 || !(cec_irq & DP_CEC_IRQ))
                goto unlock;

        drm_dp_cec_handle_irq(aux);
        drm_dp_dpcd_writeb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1, DP_CEC_IRQ);
unlock:
        mutex_unlock(&aux->cec.lock);
}
EXPORT_SYMBOL(drm_dp_cec_irq);

static bool drm_dp_cec_cap(struct drm_dp_aux *aux, u8 *cec_cap)
{
        u8 cap = 0;

        if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CAPABILITY, &cap) != 1 ||
            !(cap & DP_CEC_TUNNELING_CAPABLE))
                return false;
        if (cec_cap)
                *cec_cap = cap;
        return true;
}

/*
 * Called if the HPD was low for more than drm_dp_cec_unregister_delay
 * seconds. This unregisters the CEC adapter.
 */
static void drm_dp_cec_unregister_work(struct work_struct *work)
{
        struct drm_dp_aux *aux = container_of(work, struct drm_dp_aux,
                                              cec.unregister_work.work);

        mutex_lock(&aux->cec.lock);
        cec_unregister_adapter(aux->cec.adap);
        aux->cec.adap = NULL;
        mutex_unlock(&aux->cec.lock);
}

/*
 * A new EDID is set. If there is no CEC adapter, then create one. If
 * there was a CEC adapter, then check if the CEC adapter properties
 * were unchanged and just update the CEC physical address. Otherwise
 * unregister the old CEC adapter and create a new one.
 */
void drm_dp_cec_set_edid(struct drm_dp_aux *aux, const struct edid *edid)
{
        u32 cec_caps = CEC_CAP_DEFAULTS | CEC_CAP_NEEDS_HPD;
        unsigned int num_las = 1;
        u8 cap;

        /* No transfer function was set, so not a DP connector */
        if (!aux->transfer)
                return;

#ifndef CONFIG_MEDIA_CEC_RC
        /*
         * CEC_CAP_RC is part of CEC_CAP_DEFAULTS, but it is stripped by
         * cec_allocate_adapter() if CONFIG_MEDIA_CEC_RC is undefined.
         *
         * Do this here as well to ensure the tests against cec_caps are
         * correct.
         */
        cec_caps &= ~CEC_CAP_RC;
#endif
        cancel_delayed_work_sync(&aux->cec.unregister_work);

        mutex_lock(&aux->cec.lock);
        if (!drm_dp_cec_cap(aux, &cap)) {
                /* CEC is not supported, unregister any existing adapter */
                cec_unregister_adapter(aux->cec.adap);
                aux->cec.adap = NULL;
                goto unlock;
        }

        if (cap & DP_CEC_SNOOPING_CAPABLE)
                cec_caps |= CEC_CAP_MONITOR_ALL;
        if (cap & DP_CEC_MULTIPLE_LA_CAPABLE)
                num_las = CEC_MAX_LOG_ADDRS;

        if (aux->cec.adap) {
                if (aux->cec.adap->capabilities == cec_caps &&
                    aux->cec.adap->available_log_addrs == num_las) {
                        /* Unchanged, so just set the phys addr */
                        cec_s_phys_addr_from_edid(aux->cec.adap, edid);
                        goto unlock;
                }
                /*
                 * The capabilities changed, so unregister the old
                 * adapter first.
                 */
                cec_unregister_adapter(aux->cec.adap);
        }

        /* Create a new adapter */
        aux->cec.adap = cec_allocate_adapter(&drm_dp_cec_adap_ops,
                                             aux, aux->cec.name, cec_caps,
                                             num_las);
        if (IS_ERR(aux->cec.adap)) {
                aux->cec.adap = NULL;
                goto unlock;
        }
        if (cec_register_adapter(aux->cec.adap, aux->cec.parent)) {
                cec_delete_adapter(aux->cec.adap);
                aux->cec.adap = NULL;
        } else {
                /*
                 * Update the phys addr for the new CEC adapter. When called
                 * from drm_dp_cec_register_connector() edid == NULL, so in
                 * that case the phys addr is just invalidated.
                 */
                cec_s_phys_addr_from_edid(aux->cec.adap, edid);
        }
unlock:
        mutex_unlock(&aux->cec.lock);
}
EXPORT_SYMBOL(drm_dp_cec_set_edid);

/*
 * The EDID disappeared (likely because of the HPD going down).
 */
void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
{
        /* No transfer function was set, so not a DP connector */
        if (!aux->transfer)
                return;

        cancel_delayed_work_sync(&aux->cec.unregister_work);

        mutex_lock(&aux->cec.lock);
        if (!aux->cec.adap)
                goto unlock;

        cec_phys_addr_invalidate(aux->cec.adap);
        /*
         * We're done if we want to keep the CEC device
         * (drm_dp_cec_unregister_delay is >= NEVER_UNREG_DELAY) or if the
         * DPCD still indicates the CEC capability (expected for an integrated
         * HDMI branch device).
         */
        if (drm_dp_cec_unregister_delay < NEVER_UNREG_DELAY &&
            !drm_dp_cec_cap(aux, NULL)) {
                /*
                 * Unregister the CEC adapter after drm_dp_cec_unregister_delay
                 * seconds. This to debounce short HPD off-and-on cycles from
                 * displays.
                 */
                schedule_delayed_work(&aux->cec.unregister_work,
                                      drm_dp_cec_unregister_delay * HZ);
        }
unlock:
        mutex_unlock(&aux->cec.lock);
}
EXPORT_SYMBOL(drm_dp_cec_unset_edid);

/**
 * drm_dp_cec_register_connector() - register a new connector
 * @aux: DisplayPort AUX channel
 * @name: name of the CEC device
 * @parent: parent device
 *
 * A new connector was registered with associated CEC adapter name and
 * CEC adapter parent device. After registering the name and parent
 * drm_dp_cec_set_edid() is called to check if the connector supports
 * CEC and to register a CEC adapter if that is the case.
 */
void drm_dp_cec_register_connector(struct drm_dp_aux *aux, const char *name,
                                   struct device *parent)
{
        WARN_ON(aux->cec.adap);
        if (WARN_ON(!aux->transfer))
                return;
        aux->cec.name = name;
        aux->cec.parent = parent;
        INIT_DELAYED_WORK(&aux->cec.unregister_work,
                          drm_dp_cec_unregister_work);
}
EXPORT_SYMBOL(drm_dp_cec_register_connector);

/**
 * drm_dp_cec_unregister_connector() - unregister the CEC adapter, if any
 * @aux: DisplayPort AUX channel
 */
void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux)
{
        if (!aux->cec.adap)
                return;
        cancel_delayed_work_sync(&aux->cec.unregister_work);
        cec_unregister_adapter(aux->cec.adap);
        aux->cec.adap = NULL;
}
EXPORT_SYMBOL(drm_dp_cec_unregister_connector);