[media] uvcvideo: Extract timestamp-related statistics

[mirror_ubuntu-hirsute-kernel.git] / drivers / media / video / uvc / uvc_video.c

/*
 *      uvc_video.c  --  USB Video Class driver - Video handling
 *
 *      Copyright (C) 2005-2010
 *          Laurent Pinchart (laurent.pinchart@ideasonboard.com)
 *
 *      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);
}

/* ------------------------------------------------------------------------
 * 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_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;

        if (urb->actual_length == 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);
}

/*
 * 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 = le16_to_cpu(ep->desc.wMaxPacketSize);
        psize = (psize & 0x07ff) * (1 + ((psize >> 11) & 3));
        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 = le16_to_cpu(ep->desc.wMaxPacketSize) & 0x07ff;
        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 = 3 * 1024;
                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 = le16_to_cpu(ep->desc.wMaxPacketSize);
                        psize = (psize & 0x07ff) * (1 + ((psize >> 11) & 3));
                        if (psize >= bandwidth && psize <= best_psize) {
                                altsetting = i;
                                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;

        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. */
        uvc_queue_init(&stream->queue, stream->type, !uvc_no_drop_param);

        /* 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);
                return 0;
        }

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

        /* Commit the streaming parameters. */
        ret = uvc_commit_video(stream, &stream->ctrl);
        if (ret < 0) {
                uvc_queue_enable(&stream->queue, 0);
                return ret;
        }

        ret = uvc_init_video(stream, GFP_KERNEL);
        if (ret < 0) {
                usb_set_interface(stream->dev->udev, stream->intfnum, 0);
                uvc_queue_enable(&stream->queue, 0);
        }

        return ret;
}