uvc_video.c

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/*
 *      uvc_video.c  --  USB Video Class driver - Video handling
 *
 *      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/list.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/usb.h>
#include <linux/videodev2.h>
#include <linux/vmalloc.h>
#include <linux/wait.h>
#include <linux/atomic.h>
#include <asm/unaligned.h>

#include <media/v4l2-common.h>

#include "uvcvideo.h"

/* ------------------------------------------------------------------------
 * UVC Controls
 */

static int __uvc_query_ctrl(struct uvc_device *dev, __u8 query, __u8 unit,
            __u8 intfnum, __u8 cs, void *data, __u16 size,
            int timeout)
{
    __u8 type = USB_TYPE_CLASS | USB_RECIP_INTERFACE;
    unsigned int pipe;

    pipe = (query & 0x80) ? usb_rcvctrlpipe(dev->udev, 0)
                  : usb_sndctrlpipe(dev->udev, 0);
    type |= (query & 0x80) ? USB_DIR_IN : USB_DIR_OUT;

    return usb_control_msg(dev->udev, pipe, query, type, cs << 8,
            unit << 8 | intfnum, data, size, timeout);
}

static const char *uvc_query_name(__u8 query)
{
    switch (query) {
    case UVC_SET_CUR:
        return "SET_CUR";
    case UVC_GET_CUR:
        return "GET_CUR";
    case UVC_GET_MIN:
        return "GET_MIN";
    case UVC_GET_MAX:
        return "GET_MAX";
    case UVC_GET_RES:
        return "GET_RES";
    case UVC_GET_LEN:
        return "GET_LEN";
    case UVC_GET_INFO:
        return "GET_INFO";
    case UVC_GET_DEF:
        return "GET_DEF";
    default:
        return "<invalid>";
    }
}

int uvc_query_ctrl(struct uvc_device *dev, __u8 query, __u8 unit,
            __u8 intfnum, __u8 cs, void *data, __u16 size)
{
    int ret;

    ret = __uvc_query_ctrl(dev, query, unit, intfnum, cs, data, size,
                UVC_CTRL_CONTROL_TIMEOUT);
    if (ret != size) {
        uvc_printk(KERN_ERR, "Failed to query (%s) UVC control %u on "
            "unit %u: %d (exp. %u).\n", uvc_query_name(query), cs,
            unit, ret, size);
        return -EIO;
    }

    return 0;
}

static void uvc_fixup_video_ctrl(struct uvc_streaming *stream,
    struct uvc_streaming_control *ctrl)
{
    struct uvc_format *format = NULL;
    struct uvc_frame *frame = NULL;
    unsigned int i;

    for (i = 0; i < stream->nformats; ++i) {
        if (stream->format[i].index == ctrl->bFormatIndex) {
            format = &stream->format[i];
            break;
        }
    }

    if (format == NULL)
        return;

    for (i = 0; i < format->nframes; ++i) {
        if (format->frame[i].bFrameIndex == ctrl->bFrameIndex) {
            frame = &format->frame[i];
            break;
        }
    }

    if (frame == NULL)
        return;

    if (!(format->flags & UVC_FMT_FLAG_COMPRESSED) ||
         (ctrl->dwMaxVideoFrameSize == 0 &&
          stream->dev->uvc_version < 0x0110))
        ctrl->dwMaxVideoFrameSize =
            frame->dwMaxVideoFrameBufferSize;

    if (!(format->flags & UVC_FMT_FLAG_COMPRESSED) &&
        stream->dev->quirks & UVC_QUIRK_FIX_BANDWIDTH &&
        stream->intf->num_altsetting > 1) {
        u32 interval;
        u32 bandwidth;

        interval = (ctrl->dwFrameInterval > 100000)
             ? ctrl->dwFrameInterval
             : frame->dwFrameInterval[0];

        /* Compute a bandwidth estimation by multiplying the frame
         * size by the number of video frames per second, divide the
         * result by the number of USB frames (or micro-frames for
         * high-speed devices) per second and add the UVC header size
         * (assumed to be 12 bytes long).
         */
        bandwidth = frame->wWidth * frame->wHeight / 8 * format->bpp;
        bandwidth *= 10000000 / interval + 1;
        bandwidth /= 1000;
        if (stream->dev->udev->speed == USB_SPEED_HIGH)
            bandwidth /= 8;
        bandwidth += 12;

        /* The bandwidth estimate is too low for many cameras. Don't use
         * maximum packet sizes lower than 1024 bytes to try and work
         * around the problem. According to measurements done on two
         * different camera models, the value is high enough to get most
         * resolutions working while not preventing two simultaneous
         * VGA streams at 15 fps.
         */
        bandwidth = max_t(u32, bandwidth, 1024);

        ctrl->dwMaxPayloadTransferSize = bandwidth;
    }
}

static int uvc_get_video_ctrl(struct uvc_streaming *stream,
    struct uvc_streaming_control *ctrl, int probe, __u8 query)
{
    __u8 *data;
    __u16 size;
    int ret;

    size = stream->dev->uvc_version >= 0x0110 ? 34 : 26;
    if ((stream->dev->quirks & UVC_QUIRK_PROBE_DEF) &&
            query == UVC_GET_DEF)
        return -EIO;

    data = kmalloc(size, GFP_KERNEL);
    if (data == NULL)
        return -ENOMEM;

    ret = __uvc_query_ctrl(stream->dev, query, 0, stream->intfnum,
        probe ? UVC_VS_PROBE_CONTROL : UVC_VS_COMMIT_CONTROL, data,
        size, uvc_timeout_param);

    if ((query == UVC_GET_MIN || query == UVC_GET_MAX) && ret == 2) {
        /* Some cameras, mostly based on Bison Electronics chipsets,
         * answer a GET_MIN or GET_MAX request with the wCompQuality
         * field only.
         */
        uvc_warn_once(stream->dev, UVC_WARN_MINMAX, "UVC non "
            "compliance - GET_MIN/MAX(PROBE) incorrectly "
            "supported. Enabling workaround.\n");
        memset(ctrl, 0, sizeof *ctrl);
        ctrl->wCompQuality = le16_to_cpup((__le16 *)data);
        ret = 0;
        goto out;
    } else if (query == UVC_GET_DEF && probe == 1 && ret != size) {
        /* Many cameras don't support the GET_DEF request on their
         * video probe control. Warn once and return, the caller will
         * fall back to GET_CUR.
         */
        uvc_warn_once(stream->dev, UVC_WARN_PROBE_DEF, "UVC non "
            "compliance - GET_DEF(PROBE) not supported. "
            "Enabling workaround.\n");
        ret = -EIO;
        goto out;
    } else if (ret != size) {
        uvc_printk(KERN_ERR, "Failed to query (%u) UVC %s control : "
            "%d (exp. %u).\n", query, probe ? "probe" : "commit",
            ret, size);
        ret = -EIO;
        goto out;
    }

    ctrl->bmHint = le16_to_cpup((__le16 *)&data[0]);
    ctrl->bFormatIndex = data[2];
    ctrl->bFrameIndex = data[3];
    ctrl->dwFrameInterval = le32_to_cpup((__le32 *)&data[4]);
    ctrl->wKeyFrameRate = le16_to_cpup((__le16 *)&data[8]);
    ctrl->wPFrameRate = le16_to_cpup((__le16 *)&data[10]);
    ctrl->wCompQuality = le16_to_cpup((__le16 *)&data[12]);
    ctrl->wCompWindowSize = le16_to_cpup((__le16 *)&data[14]);
    ctrl->wDelay = le16_to_cpup((__le16 *)&data[16]);
    ctrl->dwMaxVideoFrameSize = get_unaligned_le32(&data[18]);
    ctrl->dwMaxPayloadTransferSize = get_unaligned_le32(&data[22]);

    if (size == 34) {
        ctrl->dwClockFrequency = get_unaligned_le32(&data[26]);
        ctrl->bmFramingInfo = data[30];
        ctrl->bPreferedVersion = data[31];
        ctrl->bMinVersion = data[32];
        ctrl->bMaxVersion = data[33];
    } else {
        ctrl->dwClockFrequency = stream->dev->clock_frequency;
        ctrl->bmFramingInfo = 0;
        ctrl->bPreferedVersion = 0;
        ctrl->bMinVersion = 0;
        ctrl->bMaxVersion = 0;
    }

    /* Some broken devices return null or wrong dwMaxVideoFrameSize and
     * dwMaxPayloadTransferSize fields. Try to get the value from the
     * format and frame descriptors.
     */
    uvc_fixup_video_ctrl(stream, ctrl);
    ret = 0;

out:
    kfree(data);
    return ret;
}

static int uvc_set_video_ctrl(struct uvc_streaming *stream,
    struct uvc_streaming_control *ctrl, int probe)
{
    __u8 *data;
    __u16 size;
    int ret;

    size = stream->dev->uvc_version >= 0x0110 ? 34 : 26;
    data = kzalloc(size, GFP_KERNEL);
    if (data == NULL)
        return -ENOMEM;

    *(__le16 *)&data[0] = cpu_to_le16(ctrl->bmHint);
    data[2] = ctrl->bFormatIndex;
    data[3] = ctrl->bFrameIndex;
    *(__le32 *)&data[4] = cpu_to_le32(ctrl->dwFrameInterval);
    *(__le16 *)&data[8] = cpu_to_le16(ctrl->wKeyFrameRate);
    *(__le16 *)&data[10] = cpu_to_le16(ctrl->wPFrameRate);
    *(__le16 *)&data[12] = cpu_to_le16(ctrl->wCompQuality);
    *(__le16 *)&data[14] = cpu_to_le16(ctrl->wCompWindowSize);
    *(__le16 *)&data[16] = cpu_to_le16(ctrl->wDelay);
    put_unaligned_le32(ctrl->dwMaxVideoFrameSize, &data[18]);
    put_unaligned_le32(ctrl->dwMaxPayloadTransferSize, &data[22]);

    if (size == 34) {
        put_unaligned_le32(ctrl->dwClockFrequency, &data[26]);
        data[30] = ctrl->bmFramingInfo;
        data[31] = ctrl->bPreferedVersion;
        data[32] = ctrl->bMinVersion;
        data[33] = ctrl->bMaxVersion;
    }

    ret = __uvc_query_ctrl(stream->dev, UVC_SET_CUR, 0, stream->intfnum,
        probe ? UVC_VS_PROBE_CONTROL : UVC_VS_COMMIT_CONTROL, data,
        size, uvc_timeout_param);
    if (ret != size) {
        uvc_printk(KERN_ERR, "Failed to set UVC %s control : "
            "%d (exp. %u).\n", probe ? "probe" : "commit",
            ret, size);
        ret = -EIO;
    }

    kfree(data);
    return ret;
}

int uvc_probe_video(struct uvc_streaming *stream,
    struct uvc_streaming_control *probe)
{
    struct uvc_streaming_control probe_min, probe_max;
    __u16 bandwidth;
    unsigned int i;
    int ret;

    /* Perform probing. The device should adjust the requested values
     * according to its capabilities. However, some devices, namely the
     * first generation UVC Logitech webcams, don't implement the Video
     * Probe control properly, and just return the needed bandwidth. For
     * that reason, if the needed bandwidth exceeds the maximum available
     * bandwidth, try to lower the quality.
     */
    ret = uvc_set_video_ctrl(stream, probe, 1);
    if (ret < 0)
        goto done;

    /* Get the minimum and maximum values for compression settings. */
    if (!(stream->dev->quirks & UVC_QUIRK_PROBE_MINMAX)) {
        ret = uvc_get_video_ctrl(stream, &probe_min, 1, UVC_GET_MIN);
        if (ret < 0)
            goto done;
        ret = uvc_get_video_ctrl(stream, &probe_max, 1, UVC_GET_MAX);
        if (ret < 0)
            goto done;

        probe->wCompQuality = probe_max.wCompQuality;
    }

    for (i = 0; i < 2; ++i) {
        ret = uvc_set_video_ctrl(stream, probe, 1);
        if (ret < 0)
            goto done;
        ret = uvc_get_video_ctrl(stream, probe, 1, UVC_GET_CUR);
        if (ret < 0)
            goto done;

        if (stream->intf->num_altsetting == 1)
            break;

        bandwidth = probe->dwMaxPayloadTransferSize;
        if (bandwidth <= stream->maxpsize)
            break;

        if (stream->dev->quirks & UVC_QUIRK_PROBE_MINMAX) {
            ret = -ENOSPC;
            goto done;
        }

        /* TODO: negotiate compression parameters */
        probe->wKeyFrameRate = probe_min.wKeyFrameRate;
        probe->wPFrameRate = probe_min.wPFrameRate;
        probe->wCompQuality = probe_max.wCompQuality;
        probe->wCompWindowSize = probe_min.wCompWindowSize;
    }

done:
    return ret;
}

static int uvc_commit_video(struct uvc_streaming *stream,
                struct uvc_streaming_control *probe)
{
    return uvc_set_video_ctrl(stream, probe, 0);
}

/* -----------------------------------------------------------------------------
 * Clocks and timestamps
 */

static void
uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
               const __u8 *data, int len)
{
    struct uvc_clock_sample *sample;
    unsigned int header_size;
    bool has_pts = false;
    bool has_scr = false;
    unsigned long flags;
    struct timespec ts;
    u16 host_sof;
    u16 dev_sof;

    switch (data[1] & (UVC_STREAM_PTS | UVC_STREAM_SCR)) {
    case UVC_STREAM_PTS | UVC_STREAM_SCR:
        header_size = 12;
        has_pts = true;
        has_scr = true;
        break;
    case UVC_STREAM_PTS:
        header_size = 6;
        has_pts = true;
        break;
    case UVC_STREAM_SCR:
        header_size = 8;
        has_scr = true;
        break;
    default:
        header_size = 2;
        break;
    }

    /* Check for invalid headers. */
    if (len < header_size)
        return;

    /* Extract the timestamps:
     *
     * - store the frame PTS in the buffer structure
     * - if the SCR field is present, retrieve the host SOF counter and
     *   kernel timestamps and store them with the SCR STC and SOF fields
     *   in the ring buffer
     */
    if (has_pts && buf != NULL)
        buf->pts = get_unaligned_le32(&data[2]);

    if (!has_scr)
        return;

    /* To limit the amount of data, drop SCRs with an SOF identical to the
     * previous one.
     */
    dev_sof = get_unaligned_le16(&data[header_size - 2]);
    if (dev_sof == stream->clock.last_sof)
        return;

    stream->clock.last_sof = dev_sof;

    host_sof = usb_get_current_frame_number(stream->dev->udev);
    ktime_get_ts(&ts);

    /* The UVC specification allows device implementations that can't obtain
     * the USB frame number to keep their own frame counters as long as they
     * match the size and frequency of the frame number associated with USB
     * SOF tokens. The SOF values sent by such devices differ from the USB
     * SOF tokens by a fixed offset that needs to be estimated and accounted
     * for to make timestamp recovery as accurate as possible.
     *
     * The offset is estimated the first time a device SOF value is received
     * as the difference between the host and device SOF values. As the two
     * SOF values can differ slightly due to transmission delays, consider
     * that the offset is null if the difference is not higher than 10 ms
     * (negative differences can not happen and are thus considered as an
     * offset). The video commit control wDelay field should be used to
     * compute a dynamic threshold instead of using a fixed 10 ms value, but
     * devices don't report reliable wDelay values.
     *
     * See uvc_video_clock_host_sof() for an explanation regarding why only
     * the 8 LSBs of the delta are kept.
     */
    if (stream->clock.sof_offset == (u16)-1) {
        u16 delta_sof = (host_sof - dev_sof) & 255;
        if (delta_sof >= 10)
            stream->clock.sof_offset = delta_sof;
        else
            stream->clock.sof_offset = 0;
    }

    dev_sof = (dev_sof + stream->clock.sof_offset) & 2047;

    spin_lock_irqsave(&stream->clock.lock, flags);

    sample = &stream->clock.samples[stream->clock.head];
    sample->dev_stc = get_unaligned_le32(&data[header_size - 6]);
    sample->dev_sof = dev_sof;
    sample->host_sof = host_sof;
    sample->host_ts = ts;

    /* Update the sliding window head and count. */
    stream->clock.head = (stream->clock.head + 1) % stream->clock.size;

    if (stream->clock.count < stream->clock.size)
        stream->clock.count++;

    spin_unlock_irqrestore(&stream->clock.lock, flags);
}

static void uvc_video_clock_reset(struct uvc_streaming *stream)
{
    struct uvc_clock *clock = &stream->clock;

    clock->head = 0;
    clock->count = 0;
    clock->last_sof = -1;
    clock->sof_offset = -1;
}

static int uvc_video_clock_init(struct uvc_streaming *stream)
{
    struct uvc_clock *clock = &stream->clock;

    spin_lock_init(&clock->lock);
    clock->size = 32;

    clock->samples = kmalloc(clock->size * sizeof(*clock->samples),
                 GFP_KERNEL);
    if (clock->samples == NULL)
        return -ENOMEM;

    uvc_video_clock_reset(stream);

    return 0;
}

static void uvc_video_clock_cleanup(struct uvc_streaming *stream)
{
    kfree(stream->clock.samples);
    stream->clock.samples = NULL;
}

/*
 * uvc_video_clock_host_sof - Return the host SOF value for a clock sample
 *
 * Host SOF counters reported by usb_get_current_frame_number() usually don't
 * cover the whole 11-bits SOF range (0-2047) but are limited to the HCI frame
 * schedule window. They can be limited to 8, 9 or 10 bits depending on the host
 * controller and its configuration.
 *
 * We thus need to recover the SOF value corresponding to the host frame number.
 * As the device and host frame numbers are sampled in a short interval, the
 * difference between their values should be equal to a small delta plus an
 * integer multiple of 256 caused by the host frame number limited precision.
 *
 * To obtain the recovered host SOF value, compute the small delta by masking
 * the high bits of the host frame counter and device SOF difference and add it
 * to the device SOF value.
 */
static u16 uvc_video_clock_host_sof(const struct uvc_clock_sample *sample)
{
    /* The delta value can be negative. */
    s8 delta_sof;

    delta_sof = (sample->host_sof - sample->dev_sof) & 255;

    return (sample->dev_sof + delta_sof) & 2047;
}

/*
 * uvc_video_clock_update - Update the buffer timestamp
 *
 * This function converts the buffer PTS timestamp to the host clock domain by
 * going through the USB SOF clock domain and stores the result in the V4L2
 * buffer timestamp field.
 *
 * The relationship between the device clock and the host clock isn't known.
 * However, the device and the host share the common USB SOF clock which can be
 * used to recover that relationship.
 *
 * The relationship between the device clock and the USB SOF clock is considered
 * to be linear over the clock samples sliding window and is given by
 *
 * SOF = m * PTS + p
 *
 * Several methods to compute the slope (m) and intercept (p) can be used. As
 * the clock drift should be small compared to the sliding window size, we
 * assume that the line that goes through the points at both ends of the window
 * is a good approximation. Naming those points P1 and P2, we get
 *
 * SOF = (SOF2 - SOF1) / (STC2 - STC1) * PTS
 *     + (SOF1 * STC2 - SOF2 * STC1) / (STC2 - STC1)
 *
 * or
 *
 * SOF = ((SOF2 - SOF1) * PTS + SOF1 * STC2 - SOF2 * STC1) / (STC2 - STC1)   (1)
 *
 * to avoid loosing precision in the division. Similarly, the host timestamp is
 * computed with
 *
 * TS = ((TS2 - TS1) * PTS + TS1 * SOF2 - TS2 * SOF1) / (SOF2 - SOF1)        (2)
 *
 * SOF values are coded on 11 bits by USB. We extend their precision with 16
 * decimal bits, leading to a 11.16 coding.
 *
 * TODO: To avoid surprises with device clock values, PTS/STC timestamps should
 * be normalized using the nominal device clock frequency reported through the
 * UVC descriptors.
 *
 * Both the PTS/STC and SOF counters roll over, after a fixed but device
 * specific amount of time for PTS/STC and after 2048ms for SOF. As long as the
 * sliding window size is smaller than the rollover period, differences computed
 * on unsigned integers will produce the correct result. However, the p term in
 * the linear relations will be miscomputed.
 *
 * To fix the issue, we subtract a constant from the PTS and STC values to bring
 * PTS to half the 32 bit STC range. The sliding window STC values then fit into
 * the 32 bit range without any rollover.
 *
 * Similarly, we add 2048 to the device SOF values to make sure that the SOF
 * computed by (1) will never be smaller than 0. This offset is then compensated
 * by adding 2048 to the SOF values used in (2). However, this doesn't prevent
 * rollovers between (1) and (2): the SOF value computed by (1) can be slightly
 * lower than 4096, and the host SOF counters can have rolled over to 2048. This
 * case is handled by subtracting 2048 from the SOF value if it exceeds the host
 * SOF value at the end of the sliding window.
 *
 * Finally we subtract a constant from the host timestamps to bring the first
 * timestamp of the sliding window to 1s.
 */
void uvc_video_clock_update(struct uvc_streaming *stream,
                struct v4l2_buffer *v4l2_buf,
                struct uvc_buffer *buf)
{
    struct uvc_clock *clock = &stream->clock;
    struct uvc_clock_sample *first;
    struct uvc_clock_sample *last;
    unsigned long flags;
    struct timespec ts;
    u32 delta_stc;
    u32 y1, y2;
    u32 x1, x2;
    u32 mean;
    u32 sof;
    u32 div;
    u32 rem;
    u64 y;

    spin_lock_irqsave(&clock->lock, flags);

    if (clock->count < clock->size)
        goto done;

    first = &clock->samples[clock->head];
    last = &clock->samples[(clock->head - 1) % clock->size];

    /* First step, PTS to SOF conversion. */
    delta_stc = buf->pts - (1UL << 31);
    x1 = first->dev_stc - delta_stc;
    x2 = last->dev_stc - delta_stc;
    if (x1 == x2)
        goto done;

    y1 = (first->dev_sof + 2048) << 16;
    y2 = (last->dev_sof + 2048) << 16;
    if (y2 < y1)
        y2 += 2048 << 16;

    y = (u64)(y2 - y1) * (1ULL << 31) + (u64)y1 * (u64)x2
      - (u64)y2 * (u64)x1;
    y = div_u64(y, x2 - x1);

    sof = y;

    uvc_trace(UVC_TRACE_CLOCK, "%s: PTS %u y %llu.%06llu SOF %u.%06llu "
          "(x1 %u x2 %u y1 %u y2 %u SOF offset %u)\n",
          stream->dev->name, buf->pts,
          y >> 16, div_u64((y & 0xffff) * 1000000, 65536),
          sof >> 16, div_u64(((u64)sof & 0xffff) * 1000000LLU, 65536),
          x1, x2, y1, y2, clock->sof_offset);

    /* Second step, SOF to host clock conversion. */
    x1 = (uvc_video_clock_host_sof(first) + 2048) << 16;
    x2 = (uvc_video_clock_host_sof(last) + 2048) << 16;
    if (x2 < x1)
        x2 += 2048 << 16;
    if (x1 == x2)
        goto done;

    ts = timespec_sub(last->host_ts, first->host_ts);
    y1 = NSEC_PER_SEC;
    y2 = (ts.tv_sec + 1) * NSEC_PER_SEC + ts.tv_nsec;

    /* Interpolated and host SOF timestamps can wrap around at slightly
     * different times. Handle this by adding or removing 2048 to or from
     * the computed SOF value to keep it close to the SOF samples mean
     * value.
     */
    mean = (x1 + x2) / 2;
    if (mean - (1024 << 16) > sof)
        sof += 2048 << 16;
    else if (sof > mean + (1024 << 16))
        sof -= 2048 << 16;

    y = (u64)(y2 - y1) * (u64)sof + (u64)y1 * (u64)x2
      - (u64)y2 * (u64)x1;
    y = div_u64(y, x2 - x1);

    div = div_u64_rem(y, NSEC_PER_SEC, &rem);
    ts.tv_sec = first->host_ts.tv_sec - 1 + div;
    ts.tv_nsec = first->host_ts.tv_nsec + rem;
    if (ts.tv_nsec >= NSEC_PER_SEC) {
        ts.tv_sec++;
        ts.tv_nsec -= NSEC_PER_SEC;
    }

    uvc_trace(UVC_TRACE_CLOCK, "%s: SOF %u.%06llu y %llu ts %lu.%06lu "
          "buf ts %lu.%06lu (x1 %u/%u/%u x2 %u/%u/%u y1 %u y2 %u)\n",
          stream->dev->name,
          sof >> 16, div_u64(((u64)sof & 0xffff) * 1000000LLU, 65536),
          y, ts.tv_sec, ts.tv_nsec / NSEC_PER_USEC,
          v4l2_buf->timestamp.tv_sec, v4l2_buf->timestamp.tv_usec,
          x1, first->host_sof, first->dev_sof,
          x2, last->host_sof, last->dev_sof, y1, y2);

    /* Update the V4L2 buffer. */
    v4l2_buf->timestamp.tv_sec = ts.tv_sec;
    v4l2_buf->timestamp.tv_usec = ts.tv_nsec / NSEC_PER_USEC;

done:
    spin_unlock_irqrestore(&stream->clock.lock, flags);
}

/* ------------------------------------------------------------------------
 * Stream statistics
 */

static void uvc_video_stats_decode(struct uvc_streaming *stream,
        const __u8 *data, int len)
{
    unsigned int header_size;
    bool has_pts = false;
    bool has_scr = false;
    u16 uninitialized_var(scr_sof);
    u32 uninitialized_var(scr_stc);
    u32 uninitialized_var(pts);

    if (stream->stats.stream.nb_frames == 0 &&
        stream->stats.frame.nb_packets == 0)
        ktime_get_ts(&stream->stats.stream.start_ts);

    switch (data[1] & (UVC_STREAM_PTS | UVC_STREAM_SCR)) {
    case UVC_STREAM_PTS | UVC_STREAM_SCR:
        header_size = 12;
        has_pts = true;
        has_scr = true;
        break;
    case UVC_STREAM_PTS:
        header_size = 6;
        has_pts = true;
        break;
    case UVC_STREAM_SCR:
        header_size = 8;
        has_scr = true;
        break;
    default:
        header_size = 2;
        break;
    }

    /* Check for invalid headers. */
    if (len < header_size || data[0] < header_size) {
        stream->stats.frame.nb_invalid++;
        return;
    }

    /* Extract the timestamps. */
    if (has_pts)
        pts = get_unaligned_le32(&data[2]);

    if (has_scr) {
        scr_stc = get_unaligned_le32(&data[header_size - 6]);
        scr_sof = get_unaligned_le16(&data[header_size - 2]);
    }

    /* Is PTS constant through the whole frame ? */
    if (has_pts && stream->stats.frame.nb_pts) {
        if (stream->stats.frame.pts != pts) {
            stream->stats.frame.nb_pts_diffs++;
            stream->stats.frame.last_pts_diff =
                stream->stats.frame.nb_packets;
        }
    }

    if (has_pts) {
        stream->stats.frame.nb_pts++;
        stream->stats.frame.pts = pts;
    }

    /* Do all frames have a PTS in their first non-empty packet, or before
     * their first empty packet ?
     */
    if (stream->stats.frame.size == 0) {
        if (len > header_size)
            stream->stats.frame.has_initial_pts = has_pts;
        if (len == header_size && has_pts)
            stream->stats.frame.has_early_pts = true;
    }

    /* Do the SCR.STC and SCR.SOF fields vary through the frame ? */
    if (has_scr && stream->stats.frame.nb_scr) {
        if (stream->stats.frame.scr_stc != scr_stc)
            stream->stats.frame.nb_scr_diffs++;
    }

    if (has_scr) {
        /* Expand the SOF counter to 32 bits and store its value. */
        if (stream->stats.stream.nb_frames > 0 ||
            stream->stats.frame.nb_scr > 0)
            stream->stats.stream.scr_sof_count +=
                (scr_sof - stream->stats.stream.scr_sof) % 2048;
        stream->stats.stream.scr_sof = scr_sof;

        stream->stats.frame.nb_scr++;
        stream->stats.frame.scr_stc = scr_stc;
        stream->stats.frame.scr_sof = scr_sof;

        if (scr_sof < stream->stats.stream.min_sof)
            stream->stats.stream.min_sof = scr_sof;
        if (scr_sof > stream->stats.stream.max_sof)
            stream->stats.stream.max_sof = scr_sof;
    }

    /* Record the first non-empty packet number. */
    if (stream->stats.frame.size == 0 && len > header_size)
        stream->stats.frame.first_data = stream->stats.frame.nb_packets;

    /* Update the frame size. */
    stream->stats.frame.size += len - header_size;

    /* Update the packets counters. */
    stream->stats.frame.nb_packets++;
    if (len > header_size)
        stream->stats.frame.nb_empty++;

    if (data[1] & UVC_STREAM_ERR)
        stream->stats.frame.nb_errors++;
}

static void uvc_video_stats_update(struct uvc_streaming *stream)
{
    struct uvc_stats_frame *frame = &stream->stats.frame;

    uvc_trace(UVC_TRACE_STATS, "frame %u stats: %u/%u/%u packets, "
          "%u/%u/%u pts (%searly %sinitial), %u/%u scr, "
          "last pts/stc/sof %u/%u/%u\n",
          stream->sequence, frame->first_data,
          frame->nb_packets - frame->nb_empty, frame->nb_packets,
          frame->nb_pts_diffs, frame->last_pts_diff, frame->nb_pts,
          frame->has_early_pts ? "" : "!",
          frame->has_initial_pts ? "" : "!",
          frame->nb_scr_diffs, frame->nb_scr,
          frame->pts, frame->scr_stc, frame->scr_sof);

    stream->stats.stream.nb_frames++;
    stream->stats.stream.nb_packets += stream->stats.frame.nb_packets;
    stream->stats.stream.nb_empty += stream->stats.frame.nb_empty;
    stream->stats.stream.nb_errors += stream->stats.frame.nb_errors;
    stream->stats.stream.nb_invalid += stream->stats.frame.nb_invalid;

    if (frame->has_early_pts)
        stream->stats.stream.nb_pts_early++;
    if (frame->has_initial_pts)
        stream->stats.stream.nb_pts_initial++;
    if (frame->last_pts_diff <= frame->first_data)
        stream->stats.stream.nb_pts_constant++;
    if (frame->nb_scr >= frame->nb_packets - frame->nb_empty)
        stream->stats.stream.nb_scr_count_ok++;
    if (frame->nb_scr_diffs + 1 == frame->nb_scr)
        stream->stats.stream.nb_scr_diffs_ok++;

    memset(&stream->stats.frame, 0, sizeof(stream->stats.frame));
}

size_t uvc_video_stats_dump(struct uvc_streaming *stream, char *buf,
                size_t size)
{
    unsigned int scr_sof_freq;
    unsigned int duration;
    struct timespec ts;
    size_t count = 0;

    ts.tv_sec = stream->stats.stream.stop_ts.tv_sec
          - stream->stats.stream.start_ts.tv_sec;
    ts.tv_nsec = stream->stats.stream.stop_ts.tv_nsec
           - stream->stats.stream.start_ts.tv_nsec;
    if (ts.tv_nsec < 0) {
        ts.tv_sec--;
        ts.tv_nsec += 1000000000;
    }

    /* Compute the SCR.SOF frequency estimate. At the nominal 1kHz SOF
     * frequency this will not overflow before more than 1h.
     */
    duration = ts.tv_sec * 1000 + ts.tv_nsec / 1000000;
    if (duration != 0)
        scr_sof_freq = stream->stats.stream.scr_sof_count * 1000
                 / duration;
    else
        scr_sof_freq = 0;

    count += scnprintf(buf + count, size - count,
               "frames:  %u\npackets: %u\nempty:   %u\n"
               "errors:  %u\ninvalid: %u\n",
               stream->stats.stream.nb_frames,
               stream->stats.stream.nb_packets,
               stream->stats.stream.nb_empty,
               stream->stats.stream.nb_errors,
               stream->stats.stream.nb_invalid);
    count += scnprintf(buf + count, size - count,
               "pts: %u early, %u initial, %u ok\n",
               stream->stats.stream.nb_pts_early,
               stream->stats.stream.nb_pts_initial,
               stream->stats.stream.nb_pts_constant);
    count += scnprintf(buf + count, size - count,
               "scr: %u count ok, %u diff ok\n",
               stream->stats.stream.nb_scr_count_ok,
               stream->stats.stream.nb_scr_diffs_ok);
    count += scnprintf(buf + count, size - count,
               "sof: %u <= sof <= %u, freq %u.%03u kHz\n",
               stream->stats.stream.min_sof,
               stream->stats.stream.max_sof,
               scr_sof_freq / 1000, scr_sof_freq % 1000);

    return count;
}

static void uvc_video_stats_start(struct uvc_streaming *stream)
{
    memset(&stream->stats, 0, sizeof(stream->stats));
    stream->stats.stream.min_sof = 2048;
}

static void uvc_video_stats_stop(struct uvc_streaming *stream)
{
    ktime_get_ts(&stream->stats.stream.stop_ts);
}

/* ------------------------------------------------------------------------
 * Video codecs
 */

/* Video payload decoding is handled by uvc_video_decode_start(),
 * uvc_video_decode_data() and uvc_video_decode_end().
 *
 * uvc_video_decode_start is called with URB data at the start of a bulk or
 * isochronous payload. It processes header data and returns the header size
 * in bytes if successful. If an error occurs, it returns a negative error
 * code. The following error codes have special meanings.
 *
 * - EAGAIN informs the caller that the current video buffer should be marked
 *   as done, and that the function should be called again with the same data
 *   and a new video buffer. This is used when end of frame conditions can be
 *   reliably detected at the beginning of the next frame only.
 *
 * If an error other than -EAGAIN is returned, the caller will drop the current
 * payload. No call to uvc_video_decode_data and uvc_video_decode_end will be
 * made until the next payload. -ENODATA can be used to drop the current
 * payload if no other error code is appropriate.
 *
 * uvc_video_decode_data is called for every URB with URB data. It copies the
 * data to the video buffer.
 *
 * uvc_video_decode_end is called with header data at the end of a bulk or
 * isochronous payload. It performs any additional header data processing and
 * returns 0 or a negative error code if an error occurred. As header data have
 * already been processed by uvc_video_decode_start, this functions isn't
 * required to perform sanity checks a second time.
 *
 * For isochronous transfers where a payload is always transferred in a single
 * URB, the three functions will be called in a row.
 *
 * To let the decoder process header data and update its internal state even
 * when no video buffer is available, uvc_video_decode_start must be prepared
 * to be called with a NULL buf parameter. uvc_video_decode_data and
 * uvc_video_decode_end will never be called with a NULL buffer.
 */
static int uvc_video_decode_start(struct uvc_streaming *stream,
        struct uvc_buffer *buf, const __u8 *data, int len)
{
    __u8 fid;

    /* Sanity checks:
     * - packet must be at least 2 bytes long
     * - bHeaderLength value must be at least 2 bytes (see above)
     * - bHeaderLength value can't be larger than the packet size.
     */
    if (len < 2 || data[0] < 2 || data[0] > len) {
        stream->stats.frame.nb_invalid++;
        return -EINVAL;
    }

    fid = data[1] & UVC_STREAM_FID;

    /* Increase the sequence number regardless of any buffer states, so
     * that discontinuous sequence numbers always indicate lost frames.
     */
    if (stream->last_fid != fid) {
        stream->sequence++;
        if (stream->sequence)
            uvc_video_stats_update(stream);
    }

    uvc_video_clock_decode(stream, buf, data, len);
    uvc_video_stats_decode(stream, data, len);

    /* Store the payload FID bit and return immediately when the buffer is
     * NULL.
     */
    if (buf == NULL) {
        stream->last_fid = fid;
        return -ENODATA;
    }

    /* Mark the buffer as bad if the error bit is set. */
    if (data[1] & UVC_STREAM_ERR) {
        uvc_trace(UVC_TRACE_FRAME, "Marking buffer as bad (error bit "
              "set).\n");
        buf->error = 1;
    }

    /* Synchronize to the input stream by waiting for the FID bit to be
     * toggled when the the buffer state is not UVC_BUF_STATE_ACTIVE.
     * stream->last_fid is initialized to -1, so the first isochronous
     * frame will always be in sync.
     *
     * If the device doesn't toggle the FID bit, invert stream->last_fid
     * when the EOF bit is set to force synchronisation on the next packet.
     */
    if (buf->state != UVC_BUF_STATE_ACTIVE) {
        struct timespec ts;

        if (fid == stream->last_fid) {
            uvc_trace(UVC_TRACE_FRAME, "Dropping payload (out of "
                "sync).\n");
            if ((stream->dev->quirks & UVC_QUIRK_STREAM_NO_FID) &&
                (data[1] & UVC_STREAM_EOF))
                stream->last_fid ^= UVC_STREAM_FID;
            return -ENODATA;
        }

        if (uvc_clock_param == CLOCK_MONOTONIC)
            ktime_get_ts(&ts);
        else
            ktime_get_real_ts(&ts);

        buf->buf.v4l2_buf.sequence = stream->sequence;
        buf->buf.v4l2_buf.timestamp.tv_sec = ts.tv_sec;
        buf->buf.v4l2_buf.timestamp.tv_usec =
            ts.tv_nsec / NSEC_PER_USEC;

        /* TODO: Handle PTS and SCR. */
        buf->state = UVC_BUF_STATE_ACTIVE;
    }

    /* Mark the buffer as done if we're at the beginning of a new frame.
     * End of frame detection is better implemented by checking the EOF
     * bit (FID bit toggling is delayed by one frame compared to the EOF
     * bit), but some devices don't set the bit at end of frame (and the
     * last payload can be lost anyway). We thus must check if the FID has
     * been toggled.
     *
     * stream->last_fid is initialized to -1, so the first isochronous
     * frame will never trigger an end of frame detection.
     *
     * Empty buffers (bytesused == 0) don't trigger end of frame detection
     * as it doesn't make sense to return an empty buffer. This also
     * avoids detecting end of frame conditions at FID toggling if the
     * previous payload had the EOF bit set.
     */
    if (fid != stream->last_fid && buf->bytesused != 0) {
        uvc_trace(UVC_TRACE_FRAME, "Frame complete (FID bit "
                "toggled).\n");
        buf->state = UVC_BUF_STATE_READY;
        return -EAGAIN;
    }

    stream->last_fid = fid;

    return data[0];
}

static void uvc_video_decode_data(struct uvc_streaming *stream,
        struct uvc_buffer *buf, const __u8 *data, int len)
{
    unsigned int maxlen, nbytes;
    void *mem;

    if (len <= 0)
        return;

    /* Copy the video data to the buffer. */
    maxlen = buf->length - buf->bytesused;
    mem = buf->mem + buf->bytesused;
    nbytes = min((unsigned int)len, maxlen);
    memcpy(mem, data, nbytes);
    buf->bytesused += nbytes;

    /* Complete the current frame if the buffer size was exceeded. */
    if (len > maxlen) {
        uvc_trace(UVC_TRACE_FRAME, "Frame complete (overflow).\n");
        buf->state = UVC_BUF_STATE_READY;
    }
}

static void uvc_video_decode_end(struct uvc_streaming *stream,
        struct uvc_buffer *buf, const __u8 *data, int len)
{
    /* Mark the buffer as done if the EOF marker is set. */
    if (data[1] & UVC_STREAM_EOF && buf->bytesused != 0) {
        uvc_trace(UVC_TRACE_FRAME, "Frame complete (EOF found).\n");
        if (data[0] == len)
            uvc_trace(UVC_TRACE_FRAME, "EOF in empty payload.\n");
        buf->state = UVC_BUF_STATE_READY;
        if (stream->dev->quirks & UVC_QUIRK_STREAM_NO_FID)
            stream->last_fid ^= UVC_STREAM_FID;
    }
}

/* Video payload encoding is handled by uvc_video_encode_header() and
 * uvc_video_encode_data(). Only bulk transfers are currently supported.
 *
 * uvc_video_encode_header is called at the start of a payload. It adds header
 * data to the transfer buffer and returns the header size. As the only known
 * UVC output device transfers a whole frame in a single payload, the EOF bit
 * is always set in the header.
 *
 * uvc_video_encode_data is called for every URB and copies the data from the
 * video buffer to the transfer buffer.
 */
static int uvc_video_encode_header(struct uvc_streaming *stream,
        struct uvc_buffer *buf, __u8 *data, int len)
{
    data[0] = 2;    /* Header length */
    data[1] = UVC_STREAM_EOH | UVC_STREAM_EOF
        | (stream->last_fid & UVC_STREAM_FID);
    return 2;
}

static int uvc_video_encode_data(struct uvc_streaming *stream,
        struct uvc_buffer *buf, __u8 *data, int len)
{
    struct uvc_video_queue *queue = &stream->queue;
    unsigned int nbytes;
    void *mem;

    /* Copy video data to the URB buffer. */
    mem = buf->mem + queue->buf_used;
    nbytes = min((unsigned int)len, buf->bytesused - queue->buf_used);
    nbytes = min(stream->bulk.max_payload_size - stream->bulk.payload_size,
            nbytes);
    memcpy(data, mem, nbytes);

    queue->buf_used += nbytes;

    return nbytes;
}

/* ------------------------------------------------------------------------
 * URB handling
 */

/*
 * Completion handler for video URBs.
 */
static void uvc_video_decode_isoc(struct urb *urb, struct uvc_streaming *stream,
    struct uvc_buffer *buf)
{
    u8 *mem;
    int ret, i;

    for (i = 0; i < urb->number_of_packets; ++i) {
        if (urb->iso_frame_desc[i].status < 0) {
            uvc_trace(UVC_TRACE_FRAME, "USB isochronous frame "
                "lost (%d).\n", urb->iso_frame_desc[i].status);
            /* Mark the buffer as faulty. */
            if (buf != NULL)
                buf->error = 1;
            continue;
        }

        /* Decode the payload header. */
        mem = urb->transfer_buffer + urb->iso_frame_desc[i].offset;
        do {
            ret = uvc_video_decode_start(stream, buf, mem,
                urb->iso_frame_desc[i].actual_length);
            if (ret == -EAGAIN)
                buf = uvc_queue_next_buffer(&stream->queue,
                                buf);
        } while (ret == -EAGAIN);

        if (ret < 0)
            continue;

        /* Decode the payload data. */
        uvc_video_decode_data(stream, buf, mem + ret,
            urb->iso_frame_desc[i].actual_length - ret);

        /* Process the header again. */
        uvc_video_decode_end(stream, buf, mem,
            urb->iso_frame_desc[i].actual_length);

        if (buf->state == UVC_BUF_STATE_READY) {
            if (buf->length != buf->bytesused &&
                !(stream->cur_format->flags &
                  UVC_FMT_FLAG_COMPRESSED))
                buf->error = 1;

            buf = uvc_queue_next_buffer(&stream->queue, buf);
        }
    }
}

static void uvc_video_decode_bulk(struct urb *urb, struct uvc_streaming *stream,
    struct uvc_buffer *buf)
{
    u8 *mem;
    int len, ret;

    /*
     * Ignore ZLPs if they're not part of a frame, otherwise process them
     * to trigger the end of payload detection.
     */
    if (urb->actual_length == 0 && stream->bulk.header_size == 0)
        return;

    mem = urb->transfer_buffer;
    len = urb->actual_length;
    stream->bulk.payload_size += len;

    /* If the URB is the first of its payload, decode and save the
     * header.
     */
    if (stream->bulk.header_size == 0 && !stream->bulk.skip_payload) {
        do {
            ret = uvc_video_decode_start(stream, buf, mem, len);
            if (ret == -EAGAIN)
                buf = uvc_queue_next_buffer(&stream->queue,
                                buf);
        } while (ret == -EAGAIN);

        /* If an error occurred skip the rest of the payload. */
        if (ret < 0 || buf == NULL) {
            stream->bulk.skip_payload = 1;
        } else {
            memcpy(stream->bulk.header, mem, ret);
            stream->bulk.header_size = ret;

            mem += ret;
            len -= ret;
        }
    }

    /* The buffer queue might have been cancelled while a bulk transfer
     * was in progress, so we can reach here with buf equal to NULL. Make
     * sure buf is never dereferenced if NULL.
     */

    /* Process video data. */
    if (!stream->bulk.skip_payload && buf != NULL)
        uvc_video_decode_data(stream, buf, mem, len);

    /* Detect the payload end by a URB smaller than the maximum size (or
     * a payload size equal to the maximum) and process the header again.
     */
    if (urb->actual_length < urb->transfer_buffer_length ||
        stream->bulk.payload_size >= stream->bulk.max_payload_size) {
        if (!stream->bulk.skip_payload && buf != NULL) {
            uvc_video_decode_end(stream, buf, stream->bulk.header,
                stream->bulk.payload_size);
            if (buf->state == UVC_BUF_STATE_READY)
                buf = uvc_queue_next_buffer(&stream->queue,
                                buf);
        }

        stream->bulk.header_size = 0;
        stream->bulk.skip_payload = 0;
        stream->bulk.payload_size = 0;
    }
}

static void uvc_video_encode_bulk(struct urb *urb, struct uvc_streaming *stream,
    struct uvc_buffer *buf)
{
    u8 *mem = urb->transfer_buffer;
    int len = stream->urb_size, ret;

    if (buf == NULL) {
        urb->transfer_buffer_length = 0;
        return;
    }

    /* If the URB is the first of its payload, add the header. */
    if (stream->bulk.header_size == 0) {
        ret = uvc_video_encode_header(stream, buf, mem, len);
        stream->bulk.header_size = ret;
        stream->bulk.payload_size += ret;
        mem += ret;
        len -= ret;
    }

    /* Process video data. */
    ret = uvc_video_encode_data(stream, buf, mem, len);

    stream->bulk.payload_size += ret;
    len -= ret;

    if (buf->bytesused == stream->queue.buf_used ||
        stream->bulk.payload_size == stream->bulk.max_payload_size) {
        if (buf->bytesused == stream->queue.buf_used) {
            stream->queue.buf_used = 0;
            buf->state = UVC_BUF_STATE_READY;
            buf->buf.v4l2_buf.sequence = ++stream->sequence;
            uvc_queue_next_buffer(&stream->queue, buf);
            stream->last_fid ^= UVC_STREAM_FID;
        }

        stream->bulk.header_size = 0;
        stream->bulk.payload_size = 0;
    }

    urb->transfer_buffer_length = stream->urb_size - len;
}

static void uvc_video_complete(struct urb *urb)
{
    struct uvc_streaming *stream = urb->context;
    struct uvc_video_queue *queue = &stream->queue;
    struct uvc_buffer *buf = NULL;
    unsigned long flags;
    int ret;

    switch (urb->status) {
    case 0:
        break;

    default:
        uvc_printk(KERN_WARNING, "Non-zero status (%d) in video "
            "completion handler.\n", urb->status);

    case -ENOENT:       /* usb_kill_urb() called. */
        if (stream->frozen)
            return;

    case -ECONNRESET:   /* usb_unlink_urb() called. */
    case -ESHUTDOWN:    /* The endpoint is being disabled. */
        uvc_queue_cancel(queue, urb->status == -ESHUTDOWN);
        return;
    }

    spin_lock_irqsave(&queue->irqlock, flags);
    if (!list_empty(&queue->irqqueue))
        buf = list_first_entry(&queue->irqqueue, struct uvc_buffer,
                       queue);
    spin_unlock_irqrestore(&queue->irqlock, flags);

    stream->decode(urb, stream, buf);

    if ((ret = usb_submit_urb(urb, GFP_ATOMIC)) < 0) {
        uvc_printk(KERN_ERR, "Failed to resubmit video URB (%d).\n",
            ret);
    }
}

/*
 * Free transfer buffers.
 */
static void uvc_free_urb_buffers(struct uvc_streaming *stream)
{
    unsigned int i;

    for (i = 0; i < UVC_URBS; ++i) {
        if (stream->urb_buffer[i]) {
#ifndef CONFIG_DMA_NONCOHERENT
            usb_free_coherent(stream->dev->udev, stream->urb_size,
                stream->urb_buffer[i], stream->urb_dma[i]);
#else
            kfree(stream->urb_buffer[i]);
#endif
            stream->urb_buffer[i] = NULL;
        }
    }

    stream->urb_size = 0;
}

/*
 * Allocate transfer buffers. This function can be called with buffers
 * already allocated when resuming from suspend, in which case it will
 * return without touching the buffers.
 *
 * Limit the buffer size to UVC_MAX_PACKETS bulk/isochronous packets. If the
 * system is too low on memory try successively smaller numbers of packets
 * until allocation succeeds.
 *
 * Return the number of allocated packets on success or 0 when out of memory.
 */
static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
    unsigned int size, unsigned int psize, gfp_t gfp_flags)
{
    unsigned int npackets;
    unsigned int i;

    /* Buffers are already allocated, bail out. */
    if (stream->urb_size)
        return stream->urb_size / psize;

    /* Compute the number of packets. Bulk endpoints might transfer UVC
     * payloads across multiple URBs.
     */
    npackets = DIV_ROUND_UP(size, psize);
    if (npackets > UVC_MAX_PACKETS)
        npackets = UVC_MAX_PACKETS;

    /* Retry allocations until one succeed. */
    for (; npackets > 1; npackets /= 2) {
        for (i = 0; i < UVC_URBS; ++i) {
            stream->urb_size = psize * npackets;
#ifndef CONFIG_DMA_NONCOHERENT
            stream->urb_buffer[i] = usb_alloc_coherent(
                stream->dev->udev, stream->urb_size,
                gfp_flags | __GFP_NOWARN, &stream->urb_dma[i]);
#else
            stream->urb_buffer[i] =
                kmalloc(stream->urb_size, gfp_flags | __GFP_NOWARN);
#endif
            if (!stream->urb_buffer[i]) {
                uvc_free_urb_buffers(stream);
                break;
            }
        }

        if (i == UVC_URBS) {
            uvc_trace(UVC_TRACE_VIDEO, "Allocated %u URB buffers "
                "of %ux%u bytes each.\n", UVC_URBS, npackets,
                psize);
            return npackets;
        }
    }

    uvc_trace(UVC_TRACE_VIDEO, "Failed to allocate URB buffers (%u bytes "
        "per packet).\n", psize);
    return 0;
}

/*
 * Uninitialize isochronous/bulk URBs and free transfer buffers.
 */
static void uvc_uninit_video(struct uvc_streaming *stream, int free_buffers)
{
    struct urb *urb;
    unsigned int i;

    uvc_video_stats_stop(stream);

    for (i = 0; i < UVC_URBS; ++i) {
        urb = stream->urb[i];
        if (urb == NULL)
            continue;

        usb_kill_urb(urb);
        usb_free_urb(urb);
        stream->urb[i] = NULL;
    }

    if (free_buffers)
        uvc_free_urb_buffers(stream);
}

/*
 * Compute the maximum number of bytes per interval for an endpoint.
 */
static unsigned int uvc_endpoint_max_bpi(struct usb_device *dev,
                     struct usb_host_endpoint *ep)
{
    u16 psize;

    switch (dev->speed) {
    case USB_SPEED_SUPER:
        return ep->ss_ep_comp.wBytesPerInterval;
    case USB_SPEED_HIGH:
        psize = usb_endpoint_maxp(&ep->desc);
        return (psize & 0x07ff) * (1 + ((psize >> 11) & 3));
    default:
        psize = usb_endpoint_maxp(&ep->desc);
        return psize & 0x07ff;
    }
}

/*
 * Initialize isochronous URBs and allocate transfer buffers. The packet size
 * is given by the endpoint.
 */
static int uvc_init_video_isoc(struct uvc_streaming *stream,
    struct usb_host_endpoint *ep, gfp_t gfp_flags)
{
    struct urb *urb;
    unsigned int npackets, i, j;
    u16 psize;
    u32 size;

    psize = uvc_endpoint_max_bpi(stream->dev->udev, ep);
    size = stream->ctrl.dwMaxVideoFrameSize;

    npackets = uvc_alloc_urb_buffers(stream, size, psize, gfp_flags);
    if (npackets == 0)
        return -ENOMEM;

    size = npackets * psize;

    for (i = 0; i < UVC_URBS; ++i) {
        urb = usb_alloc_urb(npackets, gfp_flags);
        if (urb == NULL) {
            uvc_uninit_video(stream, 1);
            return -ENOMEM;
        }

        urb->dev = stream->dev->udev;
        urb->context = stream;
        urb->pipe = usb_rcvisocpipe(stream->dev->udev,
                ep->desc.bEndpointAddress);
#ifndef CONFIG_DMA_NONCOHERENT
        urb->transfer_flags = URB_ISO_ASAP | URB_NO_TRANSFER_DMA_MAP;
        urb->transfer_dma = stream->urb_dma[i];
#else
        urb->transfer_flags = URB_ISO_ASAP;
#endif
        urb->interval = ep->desc.bInterval;
        urb->transfer_buffer = stream->urb_buffer[i];
        urb->complete = uvc_video_complete;
        urb->number_of_packets = npackets;
        urb->transfer_buffer_length = size;

        for (j = 0; j < npackets; ++j) {
            urb->iso_frame_desc[j].offset = j * psize;
            urb->iso_frame_desc[j].length = psize;
        }

        stream->urb[i] = urb;
    }

    return 0;
}

/*
 * Initialize bulk URBs and allocate transfer buffers. The packet size is
 * given by the endpoint.
 */
static int uvc_init_video_bulk(struct uvc_streaming *stream,
    struct usb_host_endpoint *ep, gfp_t gfp_flags)
{
    struct urb *urb;
    unsigned int npackets, pipe, i;
    u16 psize;
    u32 size;

    psize = usb_endpoint_maxp(&ep->desc) & 0x7ff;
    size = stream->ctrl.dwMaxPayloadTransferSize;
    stream->bulk.max_payload_size = size;

    npackets = uvc_alloc_urb_buffers(stream, size, psize, gfp_flags);
    if (npackets == 0)
        return -ENOMEM;

    size = npackets * psize;

    if (usb_endpoint_dir_in(&ep->desc))
        pipe = usb_rcvbulkpipe(stream->dev->udev,
                       ep->desc.bEndpointAddress);
    else
        pipe = usb_sndbulkpipe(stream->dev->udev,
                       ep->desc.bEndpointAddress);

    if (stream->type == V4L2_BUF_TYPE_VIDEO_OUTPUT)
        size = 0;

    for (i = 0; i < UVC_URBS; ++i) {
        urb = usb_alloc_urb(0, gfp_flags);
        if (urb == NULL) {
            uvc_uninit_video(stream, 1);
            return -ENOMEM;
        }

        usb_fill_bulk_urb(urb, stream->dev->udev, pipe,
            stream->urb_buffer[i], size, uvc_video_complete,
            stream);
#ifndef CONFIG_DMA_NONCOHERENT
        urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP;
        urb->transfer_dma = stream->urb_dma[i];
#endif

        stream->urb[i] = urb;
    }

    return 0;
}

/*
 * Initialize isochronous/bulk URBs and allocate transfer buffers.
 */
static int uvc_init_video(struct uvc_streaming *stream, gfp_t gfp_flags)
{
    struct usb_interface *intf = stream->intf;
    struct usb_host_endpoint *ep;
    unsigned int i;
    int ret;

    stream->sequence = -1;
    stream->last_fid = -1;
    stream->bulk.header_size = 0;
    stream->bulk.skip_payload = 0;
    stream->bulk.payload_size = 0;

    uvc_video_stats_start(stream);

    if (intf->num_altsetting > 1) {
        struct usb_host_endpoint *best_ep = NULL;
        unsigned int best_psize = UINT_MAX;
        unsigned int bandwidth;
        unsigned int uninitialized_var(altsetting);
        int intfnum = stream->intfnum;

        /* Isochronous endpoint, select the alternate setting. */
        bandwidth = stream->ctrl.dwMaxPayloadTransferSize;

        if (bandwidth == 0) {
            uvc_trace(UVC_TRACE_VIDEO, "Device requested null "
                "bandwidth, defaulting to lowest.\n");
            bandwidth = 1;
        } else {
            uvc_trace(UVC_TRACE_VIDEO, "Device requested %u "
                "B/frame bandwidth.\n", bandwidth);
        }

        for (i = 0; i < intf->num_altsetting; ++i) {
            struct usb_host_interface *alts;
            unsigned int psize;

            alts = &intf->altsetting[i];
            ep = uvc_find_endpoint(alts,
                stream->header.bEndpointAddress);
            if (ep == NULL)
                continue;

            /* Check if the bandwidth is high enough. */
            psize = uvc_endpoint_max_bpi(stream->dev->udev, ep);
            if (psize >= bandwidth && psize <= best_psize) {
                altsetting = alts->desc.bAlternateSetting;
                best_psize = psize;
                best_ep = ep;
            }
        }

        if (best_ep == NULL) {
            uvc_trace(UVC_TRACE_VIDEO, "No fast enough alt setting "
                "for requested bandwidth.\n");
            return -EIO;
        }

        uvc_trace(UVC_TRACE_VIDEO, "Selecting alternate setting %u "
            "(%u B/frame bandwidth).\n", altsetting, best_psize);

        ret = usb_set_interface(stream->dev->udev, intfnum, altsetting);
        if (ret < 0)
            return ret;

        ret = uvc_init_video_isoc(stream, best_ep, gfp_flags);
    } else {
        /* Bulk endpoint, proceed to URB initialization. */
        ep = uvc_find_endpoint(&intf->altsetting[0],
                stream->header.bEndpointAddress);
        if (ep == NULL)
            return -EIO;

        ret = uvc_init_video_bulk(stream, ep, gfp_flags);
    }

    if (ret < 0)
        return ret;

    /* Submit the URBs. */
    for (i = 0; i < UVC_URBS; ++i) {
        ret = usb_submit_urb(stream->urb[i], gfp_flags);
        if (ret < 0) {
            uvc_printk(KERN_ERR, "Failed to submit URB %u "
                    "(%d).\n", i, ret);
            uvc_uninit_video(stream, 1);
            return ret;
        }
    }

    return 0;
}

/* --------------------------------------------------------------------------
 * Suspend/resume
 */

/*
 * Stop streaming without disabling the video queue.
 *
 * To let userspace applications resume without trouble, we must not touch the
 * video buffers in any way. We mark the device as frozen to make sure the URB
 * completion handler won't try to cancel the queue when we kill the URBs.
 */
int uvc_video_suspend(struct uvc_streaming *stream)
{
    if (!uvc_queue_streaming(&stream->queue))
        return 0;

    stream->frozen = 1;
    uvc_uninit_video(stream, 0);
    usb_set_interface(stream->dev->udev, stream->intfnum, 0);
    return 0;
}

/*
 * Reconfigure the video interface and restart streaming if it was enabled
 * before suspend.
 *
 * If an error occurs, disable the video queue. This will wake all pending
 * buffers, making sure userspace applications are notified of the problem
 * instead of waiting forever.
 */
int uvc_video_resume(struct uvc_streaming *stream, int reset)
{
    int ret;

    /* If the bus has been reset on resume, set the alternate setting to 0.
     * This should be the default value, but some devices crash or otherwise
     * misbehave if they don't receive a SET_INTERFACE request before any
     * other video control request.
     */
    if (reset)
        usb_set_interface(stream->dev->udev, stream->intfnum, 0);

    stream->frozen = 0;

    uvc_video_clock_reset(stream);

    ret = uvc_commit_video(stream, &stream->ctrl);
    if (ret < 0) {
        uvc_queue_enable(&stream->queue, 0);
        return ret;
    }

    if (!uvc_queue_streaming(&stream->queue))
        return 0;

    ret = uvc_init_video(stream, GFP_NOIO);
    if (ret < 0)
        uvc_queue_enable(&stream->queue, 0);

    return ret;
}

/* ------------------------------------------------------------------------
 * Video device
 */

/*
 * Initialize the UVC video device by switching to alternate setting 0 and
 * retrieve the default format.
 *
 * Some cameras (namely the Fuji Finepix) set the format and frame
 * indexes to zero. The UVC standard doesn't clearly make this a spec
 * violation, so try to silently fix the values if possible.
 *
 * This function is called before registering the device with V4L.
 */
int uvc_video_init(struct uvc_streaming *stream)
{
    struct uvc_streaming_control *probe = &stream->ctrl;
    struct uvc_format *format = NULL;
    struct uvc_frame *frame = NULL;
    unsigned int i;
    int ret;

    if (stream->nformats == 0) {
        uvc_printk(KERN_INFO, "No supported video formats found.\n");
        return -EINVAL;
    }

    atomic_set(&stream->active, 0);

    /* Initialize the video buffers queue. */
    ret = uvc_queue_init(&stream->queue, stream->type, !uvc_no_drop_param);
    if (ret)
        return ret;

    /* Alternate setting 0 should be the default, yet the XBox Live Vision
     * Cam (and possibly other devices) crash or otherwise misbehave if
     * they don't receive a SET_INTERFACE request before any other video
     * control request.
     */
    usb_set_interface(stream->dev->udev, stream->intfnum, 0);

    /* Set the streaming probe control with default streaming parameters
     * retrieved from the device. Webcams that don't suport GET_DEF
     * requests on the probe control will just keep their current streaming
     * parameters.
     */
    if (uvc_get_video_ctrl(stream, probe, 1, UVC_GET_DEF) == 0)
        uvc_set_video_ctrl(stream, probe, 1);

    /* Initialize the streaming parameters with the probe control current
     * value. This makes sure SET_CUR requests on the streaming commit
     * control will always use values retrieved from a successful GET_CUR
     * request on the probe control, as required by the UVC specification.
     */
    ret = uvc_get_video_ctrl(stream, probe, 1, UVC_GET_CUR);
    if (ret < 0)
        return ret;

    /* Check if the default format descriptor exists. Use the first
     * available format otherwise.
     */
    for (i = stream->nformats; i > 0; --i) {
        format = &stream->format[i-1];
        if (format->index == probe->bFormatIndex)
            break;
    }

    if (format->nframes == 0) {
        uvc_printk(KERN_INFO, "No frame descriptor found for the "
            "default format.\n");
        return -EINVAL;
    }

    /* Zero bFrameIndex might be correct. Stream-based formats (including
     * MPEG-2 TS and DV) do not support frames but have a dummy frame
     * descriptor with bFrameIndex set to zero. If the default frame
     * descriptor is not found, use the first available frame.
     */
    for (i = format->nframes; i > 0; --i) {
        frame = &format->frame[i-1];
        if (frame->bFrameIndex == probe->bFrameIndex)
            break;
    }

    probe->bFormatIndex = format->index;
    probe->bFrameIndex = frame->bFrameIndex;

    stream->cur_format = format;
    stream->cur_frame = frame;

    /* Select the video decoding function */
    if (stream->type == V4L2_BUF_TYPE_VIDEO_CAPTURE) {
        if (stream->dev->quirks & UVC_QUIRK_BUILTIN_ISIGHT)
            stream->decode = uvc_video_decode_isight;
        else if (stream->intf->num_altsetting > 1)
            stream->decode = uvc_video_decode_isoc;
        else
            stream->decode = uvc_video_decode_bulk;
    } else {
        if (stream->intf->num_altsetting == 1)
            stream->decode = uvc_video_encode_bulk;
        else {
            uvc_printk(KERN_INFO, "Isochronous endpoints are not "
                "supported for video output devices.\n");
            return -EINVAL;
        }
    }

    return 0;
}

/*
 * Enable or disable the video stream.
 */
int uvc_video_enable(struct uvc_streaming *stream, int enable)
{
    int ret;

    if (!enable) {
        uvc_uninit_video(stream, 1);
        usb_set_interface(stream->dev->udev, stream->intfnum, 0);
        uvc_queue_enable(&stream->queue, 0);
        uvc_video_clock_cleanup(stream);
        return 0;
    }

    ret = uvc_video_clock_init(stream);
    if (ret < 0)
        return ret;

    ret = uvc_queue_enable(&stream->queue, 1);
    if (ret < 0)
        goto error_queue;

    /* Commit the streaming parameters. */
    ret = uvc_commit_video(stream, &stream->ctrl);
    if (ret < 0)
        goto error_commit;

    ret = uvc_init_video(stream, GFP_KERNEL);
    if (ret < 0)
        goto error_video;

    return 0;

error_video:
    usb_set_interface(stream->dev->udev, stream->intfnum, 0);
error_commit:
    uvc_queue_enable(&stream->queue, 0);
error_queue:
    uvc_video_clock_cleanup(stream);

    return ret;
}