uvc_queue.c

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/*
 *  uvc_queue.c  --  USB Video Class driver - Buffers management
 *
 *  Copyright (C) 2005-2010
 *      Laurent Pinchart ([email protected])
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 */

#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/usb.h>
#include <linux/videodev2.h>
#include <linux/vmalloc.h>
#include <linux/wait.h>
#include <linux/atomic.h>

#include "uvc.h"

/* ------------------------------------------------------------------------
 * Video buffers queue management.
 *
 * Video queues is initialized by uvc_queue_init(). The function performs
 * basic initialization of the uvc_video_queue struct and never fails.
 *
 * Video buffer allocation and freeing are performed by uvc_alloc_buffers and
 * uvc_free_buffers respectively. The former acquires the video queue lock,
 * while the later must be called with the lock held (so that allocation can
 * free previously allocated buffers). Trying to free buffers that are mapped
 * to user space will return -EBUSY.
 *
 * Video buffers are managed using two queues. However, unlike most USB video
 * drivers that use an in queue and an out queue, we use a main queue to hold
 * all queued buffers (both 'empty' and 'done' buffers), and an irq queue to
 * hold empty buffers. This design (copied from video-buf) minimizes locking
 * in interrupt, as only one queue is shared between interrupt and user
 * contexts.
 *
 * Use cases
 * ---------
 *
 * Unless stated otherwise, all operations that modify the irq buffers queue
 * are protected by the irq spinlock.
 *
 * 1. The user queues the buffers, starts streaming and dequeues a buffer.
 *
 *    The buffers are added to the main and irq queues. Both operations are
 *    protected by the queue lock, and the later is protected by the irq
 *    spinlock as well.
 *
 *    The completion handler fetches a buffer from the irq queue and fills it
 *    with video data. If no buffer is available (irq queue empty), the handler
 *    returns immediately.
 *
 *    When the buffer is full, the completion handler removes it from the irq
 *    queue, marks it as ready (UVC_BUF_STATE_DONE) and wakes its wait queue.
 *    At that point, any process waiting on the buffer will be woken up. If a
 *    process tries to dequeue a buffer after it has been marked ready, the
 *    dequeing will succeed immediately.
 *
 * 2. Buffers are queued, user is waiting on a buffer and the device gets
 *    disconnected.
 *
 *    When the device is disconnected, the kernel calls the completion handler
 *    with an appropriate status code. The handler marks all buffers in the
 *    irq queue as being erroneous (UVC_BUF_STATE_ERROR) and wakes them up so
 *    that any process waiting on a buffer gets woken up.
 *
 *    Waking up up the first buffer on the irq list is not enough, as the
 *    process waiting on the buffer might restart the dequeue operation
 *    immediately.
 *
 */

static void
uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type)
{
    mutex_init(&queue->mutex);
    spin_lock_init(&queue->irqlock);
    INIT_LIST_HEAD(&queue->mainqueue);
    INIT_LIST_HEAD(&queue->irqqueue);
    queue->type = type;
}

/*
 * Free the video buffers.
 *
 * This function must be called with the queue lock held.
 */
static int uvc_free_buffers(struct uvc_video_queue *queue)
{
    unsigned int i;

    for (i = 0; i < queue->count; ++i) {
        if (queue->buffer[i].vma_use_count != 0)
            return -EBUSY;
    }

    if (queue->count) {
        vfree(queue->mem);
        queue->count = 0;
    }

    return 0;
}

/*
 * Allocate the video buffers.
 *
 * Pages are reserved to make sure they will not be swapped, as they will be
 * filled in the URB completion handler.
 *
 * Buffers will be individually mapped, so they must all be page aligned.
 */
static int
uvc_alloc_buffers(struct uvc_video_queue *queue, unsigned int nbuffers,
          unsigned int buflength)
{
    unsigned int bufsize = PAGE_ALIGN(buflength);
    unsigned int i;
    void *mem = NULL;
    int ret;

    if (nbuffers > UVC_MAX_VIDEO_BUFFERS)
        nbuffers = UVC_MAX_VIDEO_BUFFERS;

    mutex_lock(&queue->mutex);

    if ((ret = uvc_free_buffers(queue)) < 0)
        goto done;

    /* Bail out if no buffers should be allocated. */
    if (nbuffers == 0)
        goto done;

    /* Decrement the number of buffers until allocation succeeds. */
    for (; nbuffers > 0; --nbuffers) {
        mem = vmalloc_32(nbuffers * bufsize);
        if (mem != NULL)
            break;
    }

    if (mem == NULL) {
        ret = -ENOMEM;
        goto done;
    }

    for (i = 0; i < nbuffers; ++i) {
        memset(&queue->buffer[i], 0, sizeof queue->buffer[i]);
        queue->buffer[i].buf.index = i;
        queue->buffer[i].buf.m.offset = i * bufsize;
        queue->buffer[i].buf.length = buflength;
        queue->buffer[i].buf.type = queue->type;
        queue->buffer[i].buf.sequence = 0;
        queue->buffer[i].buf.field = V4L2_FIELD_NONE;
        queue->buffer[i].buf.memory = V4L2_MEMORY_MMAP;
        queue->buffer[i].buf.flags = 0;
        init_waitqueue_head(&queue->buffer[i].wait);
    }

    queue->mem = mem;
    queue->count = nbuffers;
    queue->buf_size = bufsize;
    ret = nbuffers;

done:
    mutex_unlock(&queue->mutex);
    return ret;
}

static void __uvc_query_buffer(struct uvc_buffer *buf,
        struct v4l2_buffer *v4l2_buf)
{
    memcpy(v4l2_buf, &buf->buf, sizeof *v4l2_buf);

    if (buf->vma_use_count)
        v4l2_buf->flags |= V4L2_BUF_FLAG_MAPPED;

    switch (buf->state) {
    case UVC_BUF_STATE_ERROR:
    case UVC_BUF_STATE_DONE:
        v4l2_buf->flags |= V4L2_BUF_FLAG_DONE;
        break;
    case UVC_BUF_STATE_QUEUED:
    case UVC_BUF_STATE_ACTIVE:
        v4l2_buf->flags |= V4L2_BUF_FLAG_QUEUED;
        break;
    case UVC_BUF_STATE_IDLE:
    default:
        break;
    }
}

static int
uvc_query_buffer(struct uvc_video_queue *queue, struct v4l2_buffer *v4l2_buf)
{
    int ret = 0;

    mutex_lock(&queue->mutex);
    if (v4l2_buf->index >= queue->count) {
        ret = -EINVAL;
        goto done;
    }

    __uvc_query_buffer(&queue->buffer[v4l2_buf->index], v4l2_buf);

done:
    mutex_unlock(&queue->mutex);
    return ret;
}

/*
 * Queue a video buffer. Attempting to queue a buffer that has already been
 * queued will return -EINVAL.
 */
static int
uvc_queue_buffer(struct uvc_video_queue *queue, struct v4l2_buffer *v4l2_buf)
{
    struct uvc_buffer *buf;
    unsigned long flags;
    int ret = 0;

    uvc_trace(UVC_TRACE_CAPTURE, "Queuing buffer %u.\n", v4l2_buf->index);

    if (v4l2_buf->type != queue->type ||
        v4l2_buf->memory != V4L2_MEMORY_MMAP) {
        uvc_trace(UVC_TRACE_CAPTURE, "[E] Invalid buffer type (%u) "
            "and/or memory (%u).\n", v4l2_buf->type,
            v4l2_buf->memory);
        return -EINVAL;
    }

    mutex_lock(&queue->mutex);
    if (v4l2_buf->index >= queue->count) {
        uvc_trace(UVC_TRACE_CAPTURE, "[E] Out of range index.\n");
        ret = -EINVAL;
        goto done;
    }

    buf = &queue->buffer[v4l2_buf->index];
    if (buf->state != UVC_BUF_STATE_IDLE) {
        uvc_trace(UVC_TRACE_CAPTURE, "[E] Invalid buffer state "
            "(%u).\n", buf->state);
        ret = -EINVAL;
        goto done;
    }

    if (v4l2_buf->type == V4L2_BUF_TYPE_VIDEO_OUTPUT &&
        v4l2_buf->bytesused > buf->buf.length) {
        uvc_trace(UVC_TRACE_CAPTURE, "[E] Bytes used out of bounds.\n");
        ret = -EINVAL;
        goto done;
    }

    if (v4l2_buf->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
        buf->buf.bytesused = 0;
    else
        buf->buf.bytesused = v4l2_buf->bytesused;

    spin_lock_irqsave(&queue->irqlock, flags);
    if (queue->flags & UVC_QUEUE_DISCONNECTED) {
        spin_unlock_irqrestore(&queue->irqlock, flags);
        ret = -ENODEV;
        goto done;
    }
    buf->state = UVC_BUF_STATE_QUEUED;

    ret = (queue->flags & UVC_QUEUE_PAUSED) != 0;
    queue->flags &= ~UVC_QUEUE_PAUSED;

    list_add_tail(&buf->stream, &queue->mainqueue);
    list_add_tail(&buf->queue, &queue->irqqueue);
    spin_unlock_irqrestore(&queue->irqlock, flags);

done:
    mutex_unlock(&queue->mutex);
    return ret;
}

static int uvc_queue_waiton(struct uvc_buffer *buf, int nonblocking)
{
    if (nonblocking) {
        return (buf->state != UVC_BUF_STATE_QUEUED &&
            buf->state != UVC_BUF_STATE_ACTIVE)
            ? 0 : -EAGAIN;
    }

    return wait_event_interruptible(buf->wait,
        buf->state != UVC_BUF_STATE_QUEUED &&
        buf->state != UVC_BUF_STATE_ACTIVE);
}

/*
 * Dequeue a video buffer. If nonblocking is false, block until a buffer is
 * available.
 */
static int
uvc_dequeue_buffer(struct uvc_video_queue *queue, struct v4l2_buffer *v4l2_buf,
           int nonblocking)
{
    struct uvc_buffer *buf;
    int ret = 0;

    if (v4l2_buf->type != queue->type ||
        v4l2_buf->memory != V4L2_MEMORY_MMAP) {
        uvc_trace(UVC_TRACE_CAPTURE, "[E] Invalid buffer type (%u) "
            "and/or memory (%u).\n", v4l2_buf->type,
            v4l2_buf->memory);
        return -EINVAL;
    }

    mutex_lock(&queue->mutex);
    if (list_empty(&queue->mainqueue)) {
        uvc_trace(UVC_TRACE_CAPTURE, "[E] Empty buffer queue.\n");
        ret = -EINVAL;
        goto done;
    }

    buf = list_first_entry(&queue->mainqueue, struct uvc_buffer, stream);
    if ((ret = uvc_queue_waiton(buf, nonblocking)) < 0)
        goto done;

    uvc_trace(UVC_TRACE_CAPTURE, "Dequeuing buffer %u (%u, %u bytes).\n",
        buf->buf.index, buf->state, buf->buf.bytesused);

    switch (buf->state) {
    case UVC_BUF_STATE_ERROR:
        uvc_trace(UVC_TRACE_CAPTURE, "[W] Corrupted data "
            "(transmission error).\n");
        ret = -EIO;
    case UVC_BUF_STATE_DONE:
        buf->state = UVC_BUF_STATE_IDLE;
        break;

    case UVC_BUF_STATE_IDLE:
    case UVC_BUF_STATE_QUEUED:
    case UVC_BUF_STATE_ACTIVE:
    default:
        uvc_trace(UVC_TRACE_CAPTURE, "[E] Invalid buffer state %u "
            "(driver bug?).\n", buf->state);
        ret = -EINVAL;
        goto done;
    }

    list_del(&buf->stream);
    __uvc_query_buffer(buf, v4l2_buf);

done:
    mutex_unlock(&queue->mutex);
    return ret;
}

/*
 * Poll the video queue.
 *
 * This function implements video queue polling and is intended to be used by
 * the device poll handler.
 */
static unsigned int
uvc_queue_poll(struct uvc_video_queue *queue, struct file *file,
           poll_table *wait)
{
    struct uvc_buffer *buf;
    unsigned int mask = 0;

    mutex_lock(&queue->mutex);
    if (list_empty(&queue->mainqueue))
        goto done;

    buf = list_first_entry(&queue->mainqueue, struct uvc_buffer, stream);

    poll_wait(file, &buf->wait, wait);
    if (buf->state == UVC_BUF_STATE_DONE ||
        buf->state == UVC_BUF_STATE_ERROR)
        mask |= POLLOUT | POLLWRNORM;

done:
    mutex_unlock(&queue->mutex);
    return mask;
}

/*
 * VMA operations.
 */
static void uvc_vm_open(struct vm_area_struct *vma)
{
    struct uvc_buffer *buffer = vma->vm_private_data;
    buffer->vma_use_count++;
}

static void uvc_vm_close(struct vm_area_struct *vma)
{
    struct uvc_buffer *buffer = vma->vm_private_data;
    buffer->vma_use_count--;
}

static struct vm_operations_struct uvc_vm_ops = {
    .open       = uvc_vm_open,
    .close      = uvc_vm_close,
};

/*
 * Memory-map a buffer.
 *
 * This function implements video buffer memory mapping and is intended to be
 * used by the device mmap handler.
 */
static int
uvc_queue_mmap(struct uvc_video_queue *queue, struct vm_area_struct *vma)
{
    struct uvc_buffer *uninitialized_var(buffer);
    struct page *page;
    unsigned long addr, start, size;
    unsigned int i;
    int ret = 0;

    start = vma->vm_start;
    size = vma->vm_end - vma->vm_start;

    mutex_lock(&queue->mutex);

    for (i = 0; i < queue->count; ++i) {
        buffer = &queue->buffer[i];
        if ((buffer->buf.m.offset >> PAGE_SHIFT) == vma->vm_pgoff)
            break;
    }

    if (i == queue->count || size != queue->buf_size) {
        ret = -EINVAL;
        goto done;
    }

    /*
     * VM_IO marks the area as being an mmaped region for I/O to a
     * device. It also prevents the region from being core dumped.
     */
    vma->vm_flags |= VM_IO;

    addr = (unsigned long)queue->mem + buffer->buf.m.offset;
    while (size > 0) {
        page = vmalloc_to_page((void *)addr);
        if ((ret = vm_insert_page(vma, start, page)) < 0)
            goto done;

        start += PAGE_SIZE;
        addr += PAGE_SIZE;
        size -= PAGE_SIZE;
    }

    vma->vm_ops = &uvc_vm_ops;
    vma->vm_private_data = buffer;
    uvc_vm_open(vma);

done:
    mutex_unlock(&queue->mutex);
    return ret;
}

/*
 * Cancel the video buffers queue.
 *
 * Cancelling the queue marks all buffers on the irq queue as erroneous,
 * wakes them up and removes them from the queue.
 *
 * If the disconnect parameter is set, further calls to uvc_queue_buffer will
 * fail with -ENODEV.
 *
 * This function acquires the irq spinlock and can be called from interrupt
 * context.
 */
static void uvc_queue_cancel(struct uvc_video_queue *queue, int disconnect)
{
    struct uvc_buffer *buf;
    unsigned long flags;

    spin_lock_irqsave(&queue->irqlock, flags);
    while (!list_empty(&queue->irqqueue)) {
        buf = list_first_entry(&queue->irqqueue, struct uvc_buffer,
                       queue);
        list_del(&buf->queue);
        buf->state = UVC_BUF_STATE_ERROR;
        wake_up(&buf->wait);
    }
    /* This must be protected by the irqlock spinlock to avoid race
     * conditions between uvc_queue_buffer and the disconnection event that
     * could result in an interruptible wait in uvc_dequeue_buffer. Do not
     * blindly replace this logic by checking for the UVC_DEV_DISCONNECTED
     * state outside the queue code.
     */
    if (disconnect)
        queue->flags |= UVC_QUEUE_DISCONNECTED;
    spin_unlock_irqrestore(&queue->irqlock, flags);
}

/*
 * Enable or disable the video buffers queue.
 *
 * The queue must be enabled before starting video acquisition and must be
 * disabled after stopping it. This ensures that the video buffers queue
 * state can be properly initialized before buffers are accessed from the
 * interrupt handler.
 *
 * Enabling the video queue initializes parameters (such as sequence number,
 * sync pattern, ...). If the queue is already enabled, return -EBUSY.
 *
 * Disabling the video queue cancels the queue and removes all buffers from
 * the main queue.
 *
 * This function can't be called from interrupt context. Use
 * uvc_queue_cancel() instead.
 */
static int uvc_queue_enable(struct uvc_video_queue *queue, int enable)
{
    unsigned int i;
    int ret = 0;

    mutex_lock(&queue->mutex);
    if (enable) {
        if (uvc_queue_streaming(queue)) {
            ret = -EBUSY;
            goto done;
        }
        queue->sequence = 0;
        queue->flags |= UVC_QUEUE_STREAMING;
        queue->buf_used = 0;
    } else {
        uvc_queue_cancel(queue, 0);
        INIT_LIST_HEAD(&queue->mainqueue);

        for (i = 0; i < queue->count; ++i)
            queue->buffer[i].state = UVC_BUF_STATE_IDLE;

        queue->flags &= ~UVC_QUEUE_STREAMING;
    }

done:
    mutex_unlock(&queue->mutex);
    return ret;
}

/* called with &queue_irqlock held.. */
static struct uvc_buffer *
uvc_queue_next_buffer(struct uvc_video_queue *queue, struct uvc_buffer *buf)
{
    struct uvc_buffer *nextbuf;

    if ((queue->flags & UVC_QUEUE_DROP_INCOMPLETE) &&
        buf->buf.length != buf->buf.bytesused) {
        buf->state = UVC_BUF_STATE_QUEUED;
        buf->buf.bytesused = 0;
        return buf;
    }

    list_del(&buf->queue);
    if (!list_empty(&queue->irqqueue))
        nextbuf = list_first_entry(&queue->irqqueue, struct uvc_buffer,
                       queue);
    else
        nextbuf = NULL;

    buf->buf.sequence = queue->sequence++;
    do_gettimeofday(&buf->buf.timestamp);

    wake_up(&buf->wait);
    return nextbuf;
}

static struct uvc_buffer *uvc_queue_head(struct uvc_video_queue *queue)
{
    struct uvc_buffer *buf = NULL;

    if (!list_empty(&queue->irqqueue))
        buf = list_first_entry(&queue->irqqueue, struct uvc_buffer,
                       queue);
    else
        queue->flags |= UVC_QUEUE_PAUSED;

    return buf;
}