printf: Remove unused 'bprintf'

[drm/drm-misc.git] / drivers / media / usb / uvc / uvc_video.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *      uvc_video.c  --  USB Video Class driver - Video handling
 *
 *      Copyright (C) 2005-2010
 *          Laurent Pinchart (laurent.pinchart@ideasonboard.com)
 */

#include <linux/dma-mapping.h>
#include <linux/highmem.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/usb.h>
#include <linux/usb/hcd.h>
#include <linux/videodev2.h>
#include <linux/vmalloc.h>
#include <linux/wait.h>
#include <linux/atomic.h>
#include <linux/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;
        u8 error;
        u8 tmp;

        ret = __uvc_query_ctrl(dev, query, unit, intfnum, cs, data, size,
                                UVC_CTRL_CONTROL_TIMEOUT);
        if (likely(ret == size))
                return 0;

        if (ret != -EPIPE) {
                dev_err(&dev->udev->dev,
                        "Failed to query (%s) UVC control %u on unit %u: %d (exp. %u).\n",
                        uvc_query_name(query), cs, unit, ret, size);
                return ret < 0 ? ret : -EPIPE;
        }

        /* Reuse data[0] to request the error code. */
        tmp = *(u8 *)data;

        ret = __uvc_query_ctrl(dev, UVC_GET_CUR, 0, intfnum,
                               UVC_VC_REQUEST_ERROR_CODE_CONTROL, data, 1,
                               UVC_CTRL_CONTROL_TIMEOUT);

        error = *(u8 *)data;
        *(u8 *)data = tmp;

        if (ret != 1)
                return ret < 0 ? ret : -EPIPE;

        uvc_dbg(dev, CONTROL, "Control error %u\n", error);

        switch (error) {
        case 0:
                /* Cannot happen - we received a STALL */
                return -EPIPE;
        case 1: /* Not ready */
                return -EBUSY;
        case 2: /* Wrong state */
                return -EACCES;
        case 3: /* Power */
                return -EREMOTE;
        case 4: /* Out of range */
                return -ERANGE;
        case 5: /* Invalid unit */
        case 6: /* Invalid control */
        case 7: /* Invalid Request */
                /*
                 * The firmware has not properly implemented
                 * the control or there has been a HW error.
                 */
                return -EIO;
        case 8: /* Invalid value within range */
                return -EINVAL;
        default: /* reserved or unknown */
                break;
        }

        return -EPIPE;
}

static const struct usb_device_id elgato_cam_link_4k = {
        USB_DEVICE(0x0fd9, 0x0066)
};

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

        /*
         * The response of the Elgato Cam Link 4K is incorrect: The second byte
         * contains bFormatIndex (instead of being the second byte of bmHint).
         * The first byte is always zero. The third byte is always 1.
         *
         * The UVC 1.5 class specification defines the first five bits in the
         * bmHint bitfield. The remaining bits are reserved and should be zero.
         * Therefore a valid bmHint will be less than 32.
         *
         * Latest Elgato Cam Link 4K firmware as of 2021-03-23 needs this fix.
         * MCU: 20.02.19, FPGA: 67
         */
        if (usb_match_one_id(stream->dev->intf, &elgato_cam_link_4k) &&
            ctrl->bmHint > 255) {
                u8 corrected_format_index = ctrl->bmHint >> 8;

                uvc_dbg(stream->dev, VIDEO,
                        "Correct USB video probe response from {bmHint: 0x%04x, bFormatIndex: %u} to {bmHint: 0x%04x, bFormatIndex: %u}\n",
                        ctrl->bmHint, ctrl->bFormatIndex,
                        1, corrected_format_index);
                ctrl->bmHint = 1;
                ctrl->bFormatIndex = corrected_format_index;
        }

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

        if (format == NULL)
                return;

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

        /*
         * The "TOSHIBA Web Camera - 5M" Chicony device (04f2:b50b) seems to
         * compute the bandwidth on 16 bits and erroneously sign-extend it to
         * 32 bits, resulting in a huge bandwidth value. Detect and fix that
         * condition by setting the 16 MSBs to 0 when they're all equal to 1.
         */
        if ((ctrl->dwMaxPayloadTransferSize & 0xffff0000) == 0xffff0000)
                ctrl->dwMaxPayloadTransferSize &= ~0xffff0000;

        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- and super-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 size_t uvc_video_ctrl_size(struct uvc_streaming *stream)
{
        /*
         * Return the size of the video probe and commit controls, which depends
         * on the protocol version.
         */
        if (stream->dev->uvc_version < 0x0110)
                return 26;
        else if (stream->dev->uvc_version < 0x0150)
                return 34;
        else
                return 48;
}

static int uvc_get_video_ctrl(struct uvc_streaming *stream,
        struct uvc_streaming_control *ctrl, int probe, u8 query)
{
        u16 size = uvc_video_ctrl_size(stream);
        u8 *data;
        int ret;

        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) {
                dev_err(&stream->intf->dev,
                        "Failed to query (%u) UVC %s control : %d (exp. %u).\n",
                        query, probe ? "probe" : "commit", ret, size);
                ret = (ret == -EPROTO) ? -EPROTO : -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)
{
        u16 size = uvc_video_ctrl_size(stream);
        u8 *data;
        int ret;

        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) {
                dev_err(&stream->intf->dev,
                        "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;
        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;

                if (probe->dwMaxPayloadTransferSize <= 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 inline ktime_t uvc_video_get_time(void)
{
        if (uvc_clock_param == CLOCK_MONOTONIC)
                return ktime_get();
        else
                return ktime_get_real();
}

static void uvc_video_clock_add_sample(struct uvc_clock *clock,
                                       const struct uvc_clock_sample *sample)
{
        unsigned long flags;

        /*
         * If we write new data on the position where we had the last
         * overflow, remove the overflow pointer. There is no SOF overflow
         * in the whole circular buffer.
         */
        if (clock->head == clock->last_sof_overflow)
                clock->last_sof_overflow = -1;

        spin_lock_irqsave(&clock->lock, flags);

        if (clock->count > 0 && clock->last_sof > sample->dev_sof) {
                /*
                 * Remove data from the circular buffer that is older than the
                 * last SOF overflow. We only support one SOF overflow per
                 * circular buffer.
                 */
                if (clock->last_sof_overflow != -1)
                        clock->count = (clock->head - clock->last_sof_overflow
                                        + clock->size) % clock->size;
                clock->last_sof_overflow = clock->head;
        }

        /* Add sample. */
        clock->samples[clock->head] = *sample;
        clock->head = (clock->head + 1) % clock->size;
        clock->count = min(clock->count + 1, clock->size);

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

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;

        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. This filtering is also needed to support UVC 1.5, where
         * all the data packets of the same frame contains the same SOF. In that
         * case only the first one will match the host_sof.
         */
        sample.dev_sof = get_unaligned_le16(&data[header_size - 2]);
        if (sample.dev_sof == stream->clock.last_sof)
                return;

        sample.dev_stc = get_unaligned_le32(&data[header_size - 6]);

        /*
         * STC (Source Time Clock) is the clock used by the camera. The UVC 1.5
         * standard states that it "must be captured when the first video data
         * of a video frame is put on the USB bus". This is generally understood
         * as requiring devices to clear the payload header's SCR bit before
         * the first packet containing video data.
         *
         * Most vendors follow that interpretation, but some (namely SunplusIT
         * on some devices) always set the `UVC_STREAM_SCR` bit, fill the SCR
         * field with 0's,and expect that the driver only processes the SCR if
         * there is data in the packet.
         *
         * Ignore all the hardware timestamp information if we haven't received
         * any data for this frame yet, the packet contains no data, and both
         * STC and SOF are zero. This heuristics should be safe on compliant
         * devices. This should be safe with compliant devices, as in the very
         * unlikely case where a UVC 1.1 device would send timing information
         * only before the first packet containing data, and both STC and SOF
         * happen to be zero for a particular frame, we would only miss one
         * clock sample from many and the clock recovery algorithm wouldn't
         * suffer from this condition.
         */
        if (buf && buf->bytesused == 0 && len == header_size &&
            sample.dev_stc == 0 && sample.dev_sof == 0)
                return;

        sample.host_sof = usb_get_current_frame_number(stream->dev->udev);

        /*
         * On some devices, like the Logitech C922, the device SOF does not run
         * at a stable rate of 1kHz. For those devices use the host SOF instead.
         * In the tests performed so far, this improves the timestamp precision.
         * This is probably explained by a small packet handling jitter from the
         * host, but the exact reason hasn't been fully determined.
         */
        if (stream->dev->quirks & UVC_QUIRK_INVALID_DEVICE_SOF)
                sample.dev_sof = sample.host_sof;

        sample.host_time = uvc_video_get_time();

        /*
         * 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 = (sample.host_sof - sample.dev_sof) & 255;
                if (delta_sof >= 10)
                        stream->clock.sof_offset = delta_sof;
                else
                        stream->clock.sof_offset = 0;
        }

        sample.dev_sof = (sample.dev_sof + stream->clock.sof_offset) & 2047;
        uvc_video_clock_add_sample(&stream->clock, &sample);
        stream->clock.last_sof = sample.dev_sof;
}

static void uvc_video_clock_reset(struct uvc_clock *clock)
{
        clock->head = 0;
        clock->count = 0;
        clock->last_sof = -1;
        clock->last_sof_overflow = -1;
        clock->sof_offset = -1;
}

static int uvc_video_clock_init(struct uvc_clock *clock)
{
        spin_lock_init(&clock->lock);
        clock->size = 32;

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

        uvc_video_clock_reset(clock);

        return 0;
}

static void uvc_video_clock_cleanup(struct uvc_clock *clock)
{
        kfree(clock->samples);
        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 losing precision in the division. Similarly, the host timestamp is
 * computed with
 *
 * TS = ((TS2 - TS1) * SOF + 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 vb2_v4l2_buffer *vbuf,
                            struct uvc_buffer *buf)
{
        struct uvc_clock *clock = &stream->clock;
        struct uvc_clock_sample *first;
        struct uvc_clock_sample *last;
        unsigned long flags;
        u64 timestamp;
        u32 delta_stc;
        u32 y1;
        u32 x1, x2;
        u32 mean;
        u32 sof;
        u64 y, y2;

        if (!uvc_hw_timestamps_param)
                return;

        /*
         * We will get called from __vb2_queue_cancel() if there are buffers
         * done but not dequeued by the user, but the sample array has already
         * been released at that time. Just bail out in that case.
         */
        if (!clock->samples)
                return;

        spin_lock_irqsave(&clock->lock, flags);

        if (clock->count < 2)
                goto done;

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

        /*
         * Have at least 1/4 of a second of timestamps before we
         * try to do any calculation. Otherwise we do not have enough
         * precision. This value was determined by running Android CTS
         * on different devices.
         *
         * dev_sof runs at 1KHz, and we have a fixed point precision of
         * 16 bits.
         */
        if ((y2 - y1) < ((1000 / 4) << 16))
                goto done;

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

        sof = y;

        uvc_dbg(stream->dev, CLOCK,
                "%s: PTS %u y %llu.%06llu SOF %u.%06llu (x1 %u x2 %u y1 %u y2 %llu 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;

        y1 = NSEC_PER_SEC;
        y2 = ktime_to_ns(ktime_sub(last->host_time, first->host_time)) + y1;

        /*
         * 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);

        timestamp = ktime_to_ns(first->host_time) + y - y1;

        uvc_dbg(stream->dev, CLOCK,
                "%s: SOF %u.%06llu y %llu ts %llu buf ts %llu (x1 %u/%u/%u x2 %u/%u/%u y1 %u y2 %llu)\n",
                stream->dev->name,
                sof >> 16, div_u64(((u64)sof & 0xffff) * 1000000LLU, 65536),
                y, timestamp, vbuf->vb2_buf.timestamp,
                x1, first->host_sof, first->dev_sof,
                x2, last->host_sof, last->dev_sof, y1, y2);

        /* Update the V4L2 buffer. */
        vbuf->vb2_buf.timestamp = timestamp;

done:
        spin_unlock_irqrestore(&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 scr_sof;
        u32 scr_stc;
        u32 pts;

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

        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_dbg(stream->dev, 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;
        size_t count = 0;

        /*
         * Compute the SCR.SOF frequency estimate. At the nominal 1kHz SOF
         * frequency this will not overflow before more than 1h.
         */
        duration = ktime_ms_delta(stream->stats.stream.stop_ts,
                                  stream->stats.stream.start_ts);
        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)
{
        stream->stats.stream.stop_ts = ktime_get();
}

/* ------------------------------------------------------------------------
 * 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_dbg(stream->dev, 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 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) {
                if (fid == stream->last_fid) {
                        uvc_dbg(stream->dev, 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;
                }

                buf->buf.field = V4L2_FIELD_NONE;
                buf->buf.sequence = stream->sequence;
                buf->buf.vb2_buf.timestamp = ktime_to_ns(uvc_video_get_time());

                /* 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_dbg(stream->dev, FRAME,
                        "Frame complete (FID bit toggled)\n");
                buf->state = UVC_BUF_STATE_READY;
                return -EAGAIN;
        }

        stream->last_fid = fid;

        return data[0];
}

static inline enum dma_data_direction uvc_stream_dir(
                                struct uvc_streaming *stream)
{
        if (stream->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
                return DMA_FROM_DEVICE;
        else
                return DMA_TO_DEVICE;
}

static inline struct device *uvc_stream_to_dmadev(struct uvc_streaming *stream)
{
        return bus_to_hcd(stream->dev->udev->bus)->self.sysdev;
}

static int uvc_submit_urb(struct uvc_urb *uvc_urb, gfp_t mem_flags)
{
        /* Sync DMA. */
        dma_sync_sgtable_for_device(uvc_stream_to_dmadev(uvc_urb->stream),
                                    uvc_urb->sgt,
                                    uvc_stream_dir(uvc_urb->stream));
        return usb_submit_urb(uvc_urb->urb, mem_flags);
}

/*
 * uvc_video_decode_data_work: Asynchronous memcpy processing
 *
 * Copy URB data to video buffers in process context, releasing buffer
 * references and requeuing the URB when done.
 */
static void uvc_video_copy_data_work(struct work_struct *work)
{
        struct uvc_urb *uvc_urb = container_of(work, struct uvc_urb, work);
        unsigned int i;
        int ret;

        for (i = 0; i < uvc_urb->async_operations; i++) {
                struct uvc_copy_op *op = &uvc_urb->copy_operations[i];

                memcpy(op->dst, op->src, op->len);

                /* Release reference taken on this buffer. */
                uvc_queue_buffer_release(op->buf);
        }

        ret = uvc_submit_urb(uvc_urb, GFP_KERNEL);
        if (ret < 0)
                dev_err(&uvc_urb->stream->intf->dev,
                        "Failed to resubmit video URB (%d).\n", ret);
}

static void uvc_video_decode_data(struct uvc_urb *uvc_urb,
                struct uvc_buffer *buf, const u8 *data, int len)
{
        unsigned int active_op = uvc_urb->async_operations;
        struct uvc_copy_op *op = &uvc_urb->copy_operations[active_op];
        unsigned int maxlen;

        if (len <= 0)
                return;

        maxlen = buf->length - buf->bytesused;

        /* Take a buffer reference for async work. */
        kref_get(&buf->ref);

        op->buf = buf;
        op->src = data;
        op->dst = buf->mem + buf->bytesused;
        op->len = min_t(unsigned int, len, maxlen);

        buf->bytesused += op->len;

        /* Complete the current frame if the buffer size was exceeded. */
        if (len > maxlen) {
                uvc_dbg(uvc_urb->stream->dev, FRAME,
                        "Frame complete (overflow)\n");
                buf->error = 1;
                buf->state = UVC_BUF_STATE_READY;
        }

        uvc_urb->async_operations++;
}

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_dbg(stream->dev, FRAME, "Frame complete (EOF found)\n");
                if (data[0] == len)
                        uvc_dbg(stream->dev, 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;
}

/* ------------------------------------------------------------------------
 * Metadata
 */

/*
 * Additionally to the payload headers we also want to provide the user with USB
 * Frame Numbers and system time values. The resulting buffer is thus composed
 * of blocks, containing a 64-bit timestamp in  nanoseconds, a 16-bit USB Frame
 * Number, and a copy of the payload header.
 *
 * Ideally we want to capture all payload headers for each frame. However, their
 * number is unknown and unbound. We thus drop headers that contain no vendor
 * data and that either contain no SCR value or an SCR value identical to the
 * previous header.
 */
static void uvc_video_decode_meta(struct uvc_streaming *stream,
                                  struct uvc_buffer *meta_buf,
                                  const u8 *mem, unsigned int length)
{
        struct uvc_meta_buf *meta;
        size_t len_std = 2;
        bool has_pts, has_scr;
        unsigned long flags;
        unsigned int sof;
        ktime_t time;
        const u8 *scr;

        if (!meta_buf || length == 2)
                return;

        if (meta_buf->length - meta_buf->bytesused <
            length + sizeof(meta->ns) + sizeof(meta->sof)) {
                meta_buf->error = 1;
                return;
        }

        has_pts = mem[1] & UVC_STREAM_PTS;
        has_scr = mem[1] & UVC_STREAM_SCR;

        if (has_pts) {
                len_std += 4;
                scr = mem + 6;
        } else {
                scr = mem + 2;
        }

        if (has_scr)
                len_std += 6;

        if (stream->meta.format == V4L2_META_FMT_UVC)
                length = len_std;

        if (length == len_std && (!has_scr ||
                                  !memcmp(scr, stream->clock.last_scr, 6)))
                return;

        meta = (struct uvc_meta_buf *)((u8 *)meta_buf->mem + meta_buf->bytesused);
        local_irq_save(flags);
        time = uvc_video_get_time();
        sof = usb_get_current_frame_number(stream->dev->udev);
        local_irq_restore(flags);
        put_unaligned(ktime_to_ns(time), &meta->ns);
        put_unaligned(sof, &meta->sof);

        if (has_scr)
                memcpy(stream->clock.last_scr, scr, 6);

        meta->length = mem[0];
        meta->flags  = mem[1];
        memcpy(meta->buf, &mem[2], length - 2);
        meta_buf->bytesused += length + sizeof(meta->ns) + sizeof(meta->sof);

        uvc_dbg(stream->dev, FRAME,
                "%s(): t-sys %lluns, SOF %u, len %u, flags 0x%x, PTS %u, STC %u frame SOF %u\n",
                __func__, ktime_to_ns(time), meta->sof, meta->length,
                meta->flags,
                has_pts ? *(u32 *)meta->buf : 0,
                has_scr ? *(u32 *)scr : 0,
                has_scr ? *(u32 *)(scr + 4) & 0x7ff : 0);
}

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

/*
 * Set error flag for incomplete buffer.
 */
static void uvc_video_validate_buffer(const struct uvc_streaming *stream,
                                      struct uvc_buffer *buf)
{
        if (stream->ctrl.dwMaxVideoFrameSize != buf->bytesused &&
            !(stream->cur_format->flags & UVC_FMT_FLAG_COMPRESSED))
                buf->error = 1;
}

/*
 * Completion handler for video URBs.
 */

static void uvc_video_next_buffers(struct uvc_streaming *stream,
                struct uvc_buffer **video_buf, struct uvc_buffer **meta_buf)
{
        uvc_video_validate_buffer(stream, *video_buf);

        if (*meta_buf) {
                struct vb2_v4l2_buffer *vb2_meta = &(*meta_buf)->buf;
                const struct vb2_v4l2_buffer *vb2_video = &(*video_buf)->buf;

                vb2_meta->sequence = vb2_video->sequence;
                vb2_meta->field = vb2_video->field;
                vb2_meta->vb2_buf.timestamp = vb2_video->vb2_buf.timestamp;

                (*meta_buf)->state = UVC_BUF_STATE_READY;
                if (!(*meta_buf)->error)
                        (*meta_buf)->error = (*video_buf)->error;
                *meta_buf = uvc_queue_next_buffer(&stream->meta.queue,
                                                  *meta_buf);
        }
        *video_buf = uvc_queue_next_buffer(&stream->queue, *video_buf);
}

static void uvc_video_decode_isoc(struct uvc_urb *uvc_urb,
                        struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
{
        struct urb *urb = uvc_urb->urb;
        struct uvc_streaming *stream = uvc_urb->stream;
        u8 *mem;
        int ret, i;

        for (i = 0; i < urb->number_of_packets; ++i) {
                if (urb->iso_frame_desc[i].status < 0) {
                        uvc_dbg(stream->dev, 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)
                                uvc_video_next_buffers(stream, &buf, &meta_buf);
                } while (ret == -EAGAIN);

                if (ret < 0)
                        continue;

                uvc_video_decode_meta(stream, meta_buf, mem, ret);

                /* Decode the payload data. */
                uvc_video_decode_data(uvc_urb, 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)
                        uvc_video_next_buffers(stream, &buf, &meta_buf);
        }
}

static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
                        struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
{
        struct urb *urb = uvc_urb->urb;
        struct uvc_streaming *stream = uvc_urb->stream;
        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)
                                uvc_video_next_buffers(stream, &buf, &meta_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;

                        uvc_video_decode_meta(stream, meta_buf, mem, 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.
         */

        /* Prepare video data for processing. */
        if (!stream->bulk.skip_payload && buf != NULL)
                uvc_video_decode_data(uvc_urb, 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)
                                uvc_video_next_buffers(stream, &buf, &meta_buf);
                }

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

static void uvc_video_encode_bulk(struct uvc_urb *uvc_urb,
        struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
{
        struct urb *urb = uvc_urb->urb;
        struct uvc_streaming *stream = uvc_urb->stream;

        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.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_urb *uvc_urb = urb->context;
        struct uvc_streaming *stream = uvc_urb->stream;
        struct uvc_video_queue *queue = &stream->queue;
        struct uvc_video_queue *qmeta = &stream->meta.queue;
        struct vb2_queue *vb2_qmeta = stream->meta.vdev.queue;
        struct uvc_buffer *buf = NULL;
        struct uvc_buffer *buf_meta = NULL;
        unsigned long flags;
        int ret;

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

        default:
                dev_warn(&stream->intf->dev,
                         "Non-zero status (%d) in video completion handler.\n",
                         urb->status);
                fallthrough;
        case -ENOENT:           /* usb_poison_urb() called. */
                if (stream->frozen)
                        return;
                fallthrough;
        case -ECONNRESET:       /* usb_unlink_urb() called. */
        case -ESHUTDOWN:        /* The endpoint is being disabled. */
                uvc_queue_cancel(queue, urb->status == -ESHUTDOWN);
                if (vb2_qmeta)
                        uvc_queue_cancel(qmeta, urb->status == -ESHUTDOWN);
                return;
        }

        buf = uvc_queue_get_current_buffer(queue);

        if (vb2_qmeta) {
                spin_lock_irqsave(&qmeta->irqlock, flags);
                if (!list_empty(&qmeta->irqqueue))
                        buf_meta = list_first_entry(&qmeta->irqqueue,
                                                    struct uvc_buffer, queue);
                spin_unlock_irqrestore(&qmeta->irqlock, flags);
        }

        /* Re-initialise the URB async work. */
        uvc_urb->async_operations = 0;

        /* Sync DMA and invalidate vmap range. */
        dma_sync_sgtable_for_cpu(uvc_stream_to_dmadev(uvc_urb->stream),
                                 uvc_urb->sgt, uvc_stream_dir(stream));
        invalidate_kernel_vmap_range(uvc_urb->buffer,
                                     uvc_urb->stream->urb_size);

        /*
         * Process the URB headers, and optionally queue expensive memcpy tasks
         * to be deferred to a work queue.
         */
        stream->decode(uvc_urb, buf, buf_meta);

        /* If no async work is needed, resubmit the URB immediately. */
        if (!uvc_urb->async_operations) {
                ret = uvc_submit_urb(uvc_urb, GFP_ATOMIC);
                if (ret < 0)
                        dev_err(&stream->intf->dev,
                                "Failed to resubmit video URB (%d).\n", ret);
                return;
        }

        queue_work(stream->async_wq, &uvc_urb->work);
}

/*
 * Free transfer buffers.
 */
static void uvc_free_urb_buffers(struct uvc_streaming *stream)
{
        struct device *dma_dev = uvc_stream_to_dmadev(stream);
        struct uvc_urb *uvc_urb;

        for_each_uvc_urb(uvc_urb, stream) {
                if (!uvc_urb->buffer)
                        continue;

                dma_vunmap_noncontiguous(dma_dev, uvc_urb->buffer);
                dma_free_noncontiguous(dma_dev, stream->urb_size, uvc_urb->sgt,
                                       uvc_stream_dir(stream));

                uvc_urb->buffer = NULL;
                uvc_urb->sgt = NULL;
        }

        stream->urb_size = 0;
}

static bool uvc_alloc_urb_buffer(struct uvc_streaming *stream,
                                 struct uvc_urb *uvc_urb, gfp_t gfp_flags)
{
        struct device *dma_dev = uvc_stream_to_dmadev(stream);

        uvc_urb->sgt = dma_alloc_noncontiguous(dma_dev, stream->urb_size,
                                               uvc_stream_dir(stream),
                                               gfp_flags, 0);
        if (!uvc_urb->sgt)
                return false;
        uvc_urb->dma = uvc_urb->sgt->sgl->dma_address;

        uvc_urb->buffer = dma_vmap_noncontiguous(dma_dev, stream->urb_size,
                                                 uvc_urb->sgt);
        if (!uvc_urb->buffer) {
                dma_free_noncontiguous(dma_dev, stream->urb_size,
                                       uvc_urb->sgt,
                                       uvc_stream_dir(stream));
                uvc_urb->sgt = NULL;
                return false;
        }

        return true;
}

/*
 * 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) {
                stream->urb_size = psize * npackets;

                for (i = 0; i < UVC_URBS; ++i) {
                        struct uvc_urb *uvc_urb = &stream->uvc_urb[i];

                        if (!uvc_alloc_urb_buffer(stream, uvc_urb, gfp_flags)) {
                                uvc_free_urb_buffers(stream);
                                break;
                        }

                        uvc_urb->stream = stream;
                }

                if (i == UVC_URBS) {
                        uvc_dbg(stream->dev, VIDEO,
                                "Allocated %u URB buffers of %ux%u bytes each\n",
                                UVC_URBS, npackets, psize);
                        return npackets;
                }
        }

        uvc_dbg(stream->dev, 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_video_stop_transfer(struct uvc_streaming *stream,
                                    int free_buffers)
{
        struct uvc_urb *uvc_urb;

        uvc_video_stats_stop(stream);

        /*
         * We must poison the URBs rather than kill them to ensure that even
         * after the completion handler returns, any asynchronous workqueues
         * will be prevented from resubmitting the URBs.
         */
        for_each_uvc_urb(uvc_urb, stream)
                usb_poison_urb(uvc_urb->urb);

        flush_workqueue(stream->async_wq);

        for_each_uvc_urb(uvc_urb, stream) {
                usb_free_urb(uvc_urb->urb);
                uvc_urb->urb = NULL;
        }

        if (free_buffers)
                uvc_free_urb_buffers(stream);
}

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

        switch (dev->speed) {
        case USB_SPEED_SUPER:
        case USB_SPEED_SUPER_PLUS:
                return le16_to_cpu(ep->ss_ep_comp.wBytesPerInterval);
        default:
                psize = usb_endpoint_maxp(&ep->desc);
                psize *= usb_endpoint_maxp_mult(&ep->desc);
                return psize;
        }
}

/*
 * 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;
        struct uvc_urb *uvc_urb;
        unsigned int npackets, i;
        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_each_uvc_urb(uvc_urb, stream) {
                urb = usb_alloc_urb(npackets, gfp_flags);
                if (urb == NULL) {
                        uvc_video_stop_transfer(stream, 1);
                        return -ENOMEM;
                }

                urb->dev = stream->dev->udev;
                urb->context = uvc_urb;
                urb->pipe = usb_rcvisocpipe(stream->dev->udev,
                                ep->desc.bEndpointAddress);
                urb->transfer_flags = URB_ISO_ASAP | URB_NO_TRANSFER_DMA_MAP;
                urb->transfer_dma = uvc_urb->dma;
                urb->interval = ep->desc.bInterval;
                urb->transfer_buffer = uvc_urb->buffer;
                urb->complete = uvc_video_complete;
                urb->number_of_packets = npackets;
                urb->transfer_buffer_length = size;

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

                uvc_urb->urb = 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;
        struct uvc_urb *uvc_urb;
        unsigned int npackets, pipe;
        u16 psize;
        u32 size;

        psize = usb_endpoint_maxp(&ep->desc);
        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_each_uvc_urb(uvc_urb, stream) {
                urb = usb_alloc_urb(0, gfp_flags);
                if (urb == NULL) {
                        uvc_video_stop_transfer(stream, 1);
                        return -ENOMEM;
                }

                usb_fill_bulk_urb(urb, stream->dev->udev, pipe, uvc_urb->buffer,
                                  size, uvc_video_complete, uvc_urb);
                urb->transfer_flags = URB_NO_TRANSFER_DMA_MAP;
                urb->transfer_dma = uvc_urb->dma;

                uvc_urb->urb = urb;
        }

        return 0;
}

/*
 * Initialize isochronous/bulk URBs and allocate transfer buffers.
 */
static int uvc_video_start_transfer(struct uvc_streaming *stream,
                                    gfp_t gfp_flags)
{
        struct usb_interface *intf = stream->intf;
        struct usb_host_endpoint *ep;
        struct uvc_urb *uvc_urb;
        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 altsetting;
                int intfnum = stream->intfnum;

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

                if (bandwidth == 0) {
                        uvc_dbg(stream->dev, VIDEO,
                                "Device requested null bandwidth, defaulting to lowest\n");
                        bandwidth = 1;
                } else {
                        uvc_dbg(stream->dev, 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_dbg(stream->dev, VIDEO,
                                "No fast enough alt setting for requested bandwidth\n");
                        return -EIO;
                }

                uvc_dbg(stream->dev, VIDEO,
                        "Selecting alternate setting %u (%u B/frame bandwidth)\n",
                        altsetting, best_psize);

                /*
                 * Some devices, namely the Logitech C910 and B910, are unable
                 * to recover from a USB autosuspend, unless the alternate
                 * setting of the streaming interface is toggled.
                 */
                if (stream->dev->quirks & UVC_QUIRK_WAKE_AUTOSUSPEND) {
                        usb_set_interface(stream->dev->udev, intfnum,
                                          altsetting);
                        usb_set_interface(stream->dev->udev, intfnum, 0);
                }

                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;

                /* Reject broken descriptors. */
                if (usb_endpoint_maxp(&ep->desc) == 0)
                        return -EIO;

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

        if (ret < 0)
                return ret;

        /* Submit the URBs. */
        for_each_uvc_urb(uvc_urb, stream) {
                ret = uvc_submit_urb(uvc_urb, gfp_flags);
                if (ret < 0) {
                        dev_err(&stream->intf->dev,
                                "Failed to submit URB %u (%d).\n",
                                uvc_urb_index(uvc_urb), ret);
                        uvc_video_stop_transfer(stream, 1);
                        return ret;
                }
        }

        /*
         * The Logitech C920 temporarily forgets that it should not be adjusting
         * Exposure Absolute during init so restore controls to stored values.
         */
        if (stream->dev->quirks & UVC_QUIRK_RESTORE_CTRLS_ON_INIT)
                uvc_ctrl_restore_values(stream->dev);

        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_video_stop_transfer(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->clock);

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

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

        return uvc_video_start_transfer(stream, GFP_NOIO);
}

/* ------------------------------------------------------------------------
 * 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;
        const struct uvc_format *format = NULL;
        const struct uvc_frame *frame = NULL;
        struct uvc_urb *uvc_urb;
        unsigned int i;
        int ret;

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

        atomic_set(&stream->active, 0);

        /*
         * 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 support 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);

        /*
         * Elgato Cam Link 4k can be in a stalled state if the resolution of
         * the external source has changed while the firmware initializes.
         * Once in this state, the device is useless until it receives a
         * USB reset. It has even been observed that the stalled state will
         * continue even after unplugging the device.
         */
        if (ret == -EPROTO &&
            usb_match_one_id(stream->dev->intf, &elgato_cam_link_4k)) {
                dev_err(&stream->intf->dev, "Elgato Cam Link 4K firmware crash detected\n");
                dev_err(&stream->intf->dev, "Resetting the device, unplug and replug to recover\n");
                usb_reset_device(stream->dev->udev);
        }

        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->formats[i-1];
                if (format->index == probe->bFormatIndex)
                        break;
        }

        if (format->nframes == 0) {
                dev_info(&stream->intf->dev,
                         "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->frames[i-1];
                if (frame->bFrameIndex == probe->bFrameIndex)
                        break;
        }

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

        stream->def_format = format;
        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 {
                        dev_info(&stream->intf->dev,
                                 "Isochronous endpoints are not supported for video output devices.\n");
                        return -EINVAL;
                }
        }

        /* Prepare asynchronous work items. */
        for_each_uvc_urb(uvc_urb, stream)
                INIT_WORK(&uvc_urb->work, uvc_video_copy_data_work);

        return 0;
}

int uvc_video_start_streaming(struct uvc_streaming *stream)
{
        int ret;

        ret = uvc_video_clock_init(&stream->clock);
        if (ret < 0)
                return ret;

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

        ret = uvc_video_start_transfer(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_video_clock_cleanup(&stream->clock);

        return ret;
}

void uvc_video_stop_streaming(struct uvc_streaming *stream)
{
        uvc_video_stop_transfer(stream, 1);

        if (stream->intf->num_altsetting > 1) {
                usb_set_interface(stream->dev->udev, stream->intfnum, 0);
        } else {
                /*
                 * UVC doesn't specify how to inform a bulk-based device
                 * when the video stream is stopped. Windows sends a
                 * CLEAR_FEATURE(HALT) request to the video streaming
                 * bulk endpoint, mimic the same behaviour.
                 */
                unsigned int epnum = stream->header.bEndpointAddress
                                   & USB_ENDPOINT_NUMBER_MASK;
                unsigned int dir = stream->header.bEndpointAddress
                                 & USB_ENDPOINT_DIR_MASK;
                unsigned int pipe;

                pipe = usb_sndbulkpipe(stream->dev->udev, epnum) | dir;
                usb_clear_halt(stream->dev->udev, pipe);
        }

        uvc_video_clock_cleanup(&stream->clock);
}