/*
 * Function Control Protocol (IEC 61883-1) helper functions
 *
 * Copyright (c) Clemens Ladisch <clemens@ladisch.de>
 * Licensed under the terms of the GNU General Public License, version 2.
 */

#include <linux/device.h>
#include <linux/firewire.h>
#include <linux/firewire-constants.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/wait.h>
#include <linux/delay.h>
#include "fcp.h"
#include "lib.h"

#define CTS_AVC 0x00

#define ERROR_RETRIES   3
#define ERROR_DELAY_MS  5
#define FCP_TIMEOUT_MS  125

static DEFINE_SPINLOCK(transactions_lock);
static LIST_HEAD(transactions);

enum fcp_state {
        STATE_PENDING,
        STATE_BUS_RESET,
        STATE_COMPLETE,
};

struct fcp_transaction {
        struct list_head list;
        struct fw_unit *unit;
        void *response_buffer;
        unsigned int response_size;
        unsigned int response_match_bytes;
        enum fcp_state state;
        wait_queue_head_t wait;
};

/**
 * fcp_avc_transaction - send an AV/C command and wait for its response
 * @unit: a unit on the target device
 * @command: a buffer containing the command frame; must be DMA-able
 * @command_size: the size of @command
 * @response: a buffer for the response frame
 * @response_size: the maximum size of @response
 * @response_match_bytes: a bitmap specifying the bytes used to detect the
 *                        correct response frame
 *
 * This function sends a FCP command frame to the target and waits for the
 * corresponding response frame to be returned.
 *
 * Because it is possible for multiple FCP transactions to be active at the
 * same time, the correct response frame is detected by the value of certain
 * bytes.  These bytes must be set in @response before calling this function,
 * and the corresponding bits must be set in @response_match_bytes.
 *
 * @command and @response can point to the same buffer.
 *
 * Asynchronous operation (INTERIM, NOTIFY) is not supported at the moment.
 *
 * Returns the actual size of the response frame, or a negative error code.
 */
int fcp_avc_transaction(struct fw_unit *unit,
                        const void *command, unsigned int command_size,
                        void *response, unsigned int response_size,
                        unsigned int response_match_bytes)
{
        struct fcp_transaction t;
        int tcode, ret, tries = 0;

        t.unit = unit;
        t.response_buffer = response;
        t.response_size = response_size;
        t.response_match_bytes = response_match_bytes;
        t.state = STATE_PENDING;
        init_waitqueue_head(&t.wait);

        spin_lock_irq(&transactions_lock);
        list_add_tail(&t.list, &transactions);
        spin_unlock_irq(&transactions_lock);

        for (;;) {
                tcode = command_size == 4 ? TCODE_WRITE_QUADLET_REQUEST
                                          : TCODE_WRITE_BLOCK_REQUEST;
                ret = snd_fw_transaction(t.unit, tcode,
                                         CSR_REGISTER_BASE + CSR_FCP_COMMAND,
                                         (void *)command, command_size);
                if (ret < 0)
                        break;

                wait_event_timeout(t.wait, t.state != STATE_PENDING,
                                   msecs_to_jiffies(FCP_TIMEOUT_MS));

                if (t.state == STATE_COMPLETE) {
                        ret = t.response_size;
                        break;
                } else if (t.state == STATE_BUS_RESET) {
                        msleep(ERROR_DELAY_MS);
                } else if (++tries >= ERROR_RETRIES) {
                        dev_err(&t.unit->device, "FCP command timed out\n");
                        ret = -EIO;
                        break;
                }
        }

        spin_lock_irq(&transactions_lock);
        list_del(&t.list);
        spin_unlock_irq(&transactions_lock);

        return ret;
}
EXPORT_SYMBOL(fcp_avc_transaction);

/**
 * fcp_bus_reset - inform the target handler about a bus reset
 * @unit: the unit that might be used by fcp_avc_transaction()
 *
 * This function must be called from the driver's .update handler to inform
 * the FCP transaction handler that a bus reset has happened.  Any pending FCP
 * transactions are retried.
 */
void fcp_bus_reset(struct fw_unit *unit)
{
        struct fcp_transaction *t;

        spin_lock_irq(&transactions_lock);
        list_for_each_entry(t, &transactions, list) {
                if (t->unit == unit &&
                    t->state == STATE_PENDING) {
                        t->state = STATE_BUS_RESET;
                        wake_up(&t->wait);
                }
        }
        spin_unlock_irq(&transactions_lock);
}
EXPORT_SYMBOL(fcp_bus_reset);

/* checks whether the response matches the masked bytes in response_buffer */
static bool is_matching_response(struct fcp_transaction *transaction,
                                 const void *response, size_t length)
{
        const u8 *p1, *p2;
        unsigned int mask, i;

        p1 = response;
        p2 = transaction->response_buffer;
        mask = transaction->response_match_bytes;

        for (i = 0; ; ++i) {
                if ((mask & 1) && p1[i] != p2[i])
                        return false;
                mask >>= 1;
                if (!mask)
                        return true;
                if (--length == 0)
                        return false;
        }
}

static void fcp_response(struct fw_card *card, struct fw_request *request,
                         int tcode, int destination, int source,
                         int generation, unsigned long long offset,
                         void *data, size_t length, void *callback_data)
{
        struct fcp_transaction *t;
        unsigned long flags;

        if (length < 1 || (*(const u8 *)data & 0xf0) != CTS_AVC)
                return;

        spin_lock_irqsave(&transactions_lock, flags);
        list_for_each_entry(t, &transactions, list) {
                struct fw_device *device = fw_parent_device(t->unit);
                if (device->card != card ||
                    device->generation != generation)
                        continue;
                smp_rmb(); /* node_id vs. generation */
                if (device->node_id != source)
                        continue;

                if (t->state == STATE_PENDING &&
                    is_matching_response(t, data, length)) {
                        t->state = STATE_COMPLETE;
                        t->response_size = min((unsigned int)length,
                                               t->response_size);
                        memcpy(t->response_buffer, data, t->response_size);
                        wake_up(&t->wait);
                }
        }
        spin_unlock_irqrestore(&transactions_lock, flags);
}

static struct fw_address_handler response_register_handler = {
        .length = 0x200,
        .address_callback = fcp_response,
};

static int __init fcp_module_init(void)
{
        static const struct fw_address_region response_register_region = {
                .start = CSR_REGISTER_BASE + CSR_FCP_RESPONSE,
                .end = CSR_REGISTER_BASE + CSR_FCP_END,
        };

        fw_core_add_address_handler(&response_register_handler,
                                    &response_register_region);

        return 0;
}

static void __exit fcp_module_exit(void)
{
        WARN_ON(!list_empty(&transactions));
        fw_core_remove_address_handler(&response_register_handler);
}

module_init(fcp_module_init);
module_exit(fcp_module_exit);