text: /*
   *      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);
  }
  
  /* -----------------------------------------------------------------------------
   * Clocks and timestamps
   */
  
  static void
  uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
  		       const __u8 *data, int len)
  {
  	struct uvc_clock_sample *sample;
  	unsigned int header_size;
  	bool has_pts = false;
  	bool has_scr = false;
  	unsigned long flags;
  	struct timespec ts;
  	u16 host_sof;
  	u16 dev_sof;
  
  	switch (data[1] & (UVC_STREAM_PTS | UVC_STREAM_SCR)) {
  	case UVC_STREAM_PTS | UVC_STREAM_SCR:
  		header_size = 12;
  		has_pts = true;
  		has_scr = true;
  		break;
  	case UVC_STREAM_PTS:
  		header_size = 6;
  		has_pts = true;
  		break;
  	case UVC_STREAM_SCR:
  		header_size = 8;
  		has_scr = true;
  		break;
  	default:
  		header_size = 2;
  		break;
  	}
  
  	/* Check for invalid headers. */
  	if (len < header_size)
  		return;
  
  	/* Extract the timestamps:
  	 *
  	 * - store the frame PTS in the buffer structure
  	 * - if the SCR field is present, retrieve the host SOF counter and
  	 *   kernel timestamps and store them with the SCR STC and SOF fields
  	 *   in the ring buffer
  	 */
  	if (has_pts && buf != NULL)
  		buf->pts = get_unaligned_le32(&data[2]);
  
  	if (!has_scr)
  		return;
  
  	/* To limit the amount of data, drop SCRs with an SOF identical to the
  	 * previous one.
  	 */
  	dev_sof = get_unaligned_le16(&data[header_size - 2]);
  	if (dev_sof == stream->clock.last_sof)
  		return;
  
  	stream->clock.last_sof = dev_sof;
  
  	host_sof = usb_get_current_frame_number(stream->dev->udev);
  	ktime_get_ts(&ts);
  
  	/* The UVC specification allows device implementations that can't obtain
  	 * the USB frame number to keep their own frame counters as long as they
  	 * match the size and frequency of the frame number associated with USB
  	 * SOF tokens. The SOF values sent by such devices differ from the USB
  	 * SOF tokens by a fixed offset that needs to be estimated and accounted
  	 * for to make timestamp recovery as accurate as possible.
  	 *
  	 * The offset is estimated the first time a device SOF value is received
  	 * as the difference between the host and device SOF values. As the two
  	 * SOF values can differ slightly due to transmission delays, consider
  	 * that the offset is null if the difference is not higher than 10 ms
  	 * (negative differences can not happen and are thus considered as an
  	 * offset). The video commit control wDelay field should be used to
  	 * compute a dynamic threshold instead of using a fixed 10 ms value, but
  	 * devices don't report reliable wDelay values.
  	 *
  	 * See uvc_video_clock_host_sof() for an explanation regarding why only
  	 * the 8 LSBs of the delta are kept.
  	 */
  	if (stream->clock.sof_offset == (u16)-1) {
  		u16 delta_sof = (host_sof - dev_sof) & 255;
  		if (delta_sof >= 10)
  			stream->clock.sof_offset = delta_sof;
  		else
  			stream->clock.sof_offset = 0;
  	}
  
  	dev_sof = (dev_sof + stream->clock.sof_offset) & 2047;
  
  	spin_lock_irqsave(&stream->clock.lock, flags);
  
  	sample = &stream->clock.samples[stream->clock.head];
  	sample->dev_stc = get_unaligned_le32(&data[header_size - 6]);
  	sample->dev_sof = dev_sof;
  	sample->host_sof = host_sof;
  	sample->host_ts = ts;
  
  	/* Update the sliding window head and count. */
  	stream->clock.head = (stream->clock.head + 1) % stream->clock.size;
  
  	if (stream->clock.count < stream->clock.size)
  		stream->clock.count++;
  
  	spin_unlock_irqrestore(&stream->clock.lock, flags);
  }
  
  static void uvc_video_clock_reset(struct uvc_streaming *stream)
  {
  	struct uvc_clock *clock = &stream->clock;
  
  	clock->head = 0;
  	clock->count = 0;
  	clock->last_sof = -1;
  	clock->sof_offset = -1;
  }
  
  static int uvc_video_clock_init(struct uvc_streaming *stream)
  {
  	struct uvc_clock *clock = &stream->clock;
  
  	spin_lock_init(&clock->lock);
  	clock->size = 32;
  
  	clock->samples = kmalloc(clock->size * sizeof(*clock->samples),
  				 GFP_KERNEL);
  	if (clock->samples == NULL)
  		return -ENOMEM;
  
  	uvc_video_clock_reset(stream);
  
  	return 0;
  }
  
  static void uvc_video_clock_cleanup(struct uvc_streaming *stream)
  {
  	kfree(stream->clock.samples);
  	stream->clock.samples = NULL;
  }
  
  /*
   * uvc_video_clock_host_sof - Return the host SOF value for a clock sample
   *
   * Host SOF counters reported by usb_get_current_frame_number() usually don't
   * cover the whole 11-bits SOF range (0-2047) but are limited to the HCI frame
   * schedule window. They can be limited to 8, 9 or 10 bits depending on the host
   * controller and its configuration.
   *
   * We thus need to recover the SOF value corresponding to the host frame number.
   * As the device and host frame numbers are sampled in a short interval, the
   * difference between their values should be equal to a small delta plus an
   * integer multiple of 256 caused by the host frame number limited precision.
   *
   * To obtain the recovered host SOF value, compute the small delta by masking
   * the high bits of the host frame counter and device SOF difference and add it
   * to the device SOF value.
   */
  static u16 uvc_video_clock_host_sof(const struct uvc_clock_sample *sample)
  {
  	/* The delta value can be negative. */
  	s8 delta_sof;
  
  	delta_sof = (sample->host_sof - sample->dev_sof) & 255;
  
  	return (sample->dev_sof + delta_sof) & 2047;
  }
  
  /*
   * uvc_video_clock_update - Update the buffer timestamp
   *
   * This function converts the buffer PTS timestamp to the host clock domain by
   * going through the USB SOF clock domain and stores the result in the V4L2
   * buffer timestamp field.
   *
   * The relationship between the device clock and the host clock isn't known.
   * However, the device and the host share the common USB SOF clock which can be
   * used to recover that relationship.
   *
   * The relationship between the device clock and the USB SOF clock is considered
   * to be linear over the clock samples sliding window and is given by
   *
   * SOF = m * PTS + p
   *
   * Several methods to compute the slope (m) and intercept (p) can be used. As
   * the clock drift should be small compared to the sliding window size, we
   * assume that the line that goes through the points at both ends of the window
   * is a good approximation. Naming those points P1 and P2, we get
   *
   * SOF = (SOF2 - SOF1) / (STC2 - STC1) * PTS
   *     + (SOF1 * STC2 - SOF2 * STC1) / (STC2 - STC1)
   *
   * or
   *
   * SOF = ((SOF2 - SOF1) * PTS + SOF1 * STC2 - SOF2 * STC1) / (STC2 - STC1)   (1)
   *
   * to avoid loosing precision in the division. Similarly, the host timestamp is
   * computed with
   *
   * TS = ((TS2 - TS1) * PTS + TS1 * SOF2 - TS2 * SOF1) / (SOF2 - SOF1)	     (2)
   *
   * SOF values are coded on 11 bits by USB. We extend their precision with 16
   * decimal bits, leading to a 11.16 coding.
   *
   * TODO: To avoid surprises with device clock values, PTS/STC timestamps should
   * be normalized using the nominal device clock frequency reported through the
   * UVC descriptors.
   *
   * Both the PTS/STC and SOF counters roll over, after a fixed but device
   * specific amount of time for PTS/STC and after 2048ms for SOF. As long as the
   * sliding window size is smaller than the rollover period, differences computed
   * on unsigned integers will produce the correct result. However, the p term in
   * the linear relations will be miscomputed.
   *
   * To fix the issue, we subtract a constant from the PTS and STC values to bring
   * PTS to half the 32 bit STC range. The sliding window STC values then fit into
   * the 32 bit range without any rollover.
   *
   * Similarly, we add 2048 to the device SOF values to make sure that the SOF
   * computed by (1) will never be smaller than 0. This offset is then compensated
   * by adding 2048 to the SOF values used in (2). However, this doesn't prevent
   * rollovers between (1) and (2): the SOF value computed by (1) can be slightly
   * lower than 4096, and the host SOF counters can have rolled over to 2048. This
   * case is handled by subtracting 2048 from the SOF value if it exceeds the host
   * SOF value at the end of the sliding window.
   *
   * Finally we subtract a constant from the host timestamps to bring the first
   * timestamp of the sliding window to 1s.
   */
  void uvc_video_clock_update(struct uvc_streaming *stream,
  			    struct v4l2_buffer *v4l2_buf,
  			    struct uvc_buffer *buf)
  {
  	struct uvc_clock *clock = &stream->clock;
  	struct uvc_clock_sample *first;
  	struct uvc_clock_sample *last;
  	unsigned long flags;
  	struct timespec ts;
  	u32 delta_stc;
  	u32 y1, y2;
  	u32 x1, x2;
  	u32 mean;
  	u32 sof;
  	u32 div;
  	u32 rem;
  	u64 y;
  
  	spin_lock_irqsave(&clock->lock, flags);
  
  	if (clock->count < clock->size)
  		goto done;
  
  	first = &clock->samples[clock->head];
  	last = &clock->samples[(clock->head - 1) % clock->size];
  
  	/* First step, PTS to SOF conversion. */
  	delta_stc = buf->pts - (1UL << 31);
  	x1 = first->dev_stc - delta_stc;
  	x2 = last->dev_stc - delta_stc;
  	if (x1 == x2)
  		goto done;
  
  	y1 = (first->dev_sof + 2048) << 16;
  	y2 = (last->dev_sof + 2048) << 16;
  	if (y2 < y1)
  		y2 += 2048 << 16;
  
  	y = (u64)(y2 - y1) * (1ULL << 31) + (u64)y1 * (u64)x2
  	  - (u64)y2 * (u64)x1;
  	y = div_u64(y, x2 - x1);
  
  	sof = y;
  
  	uvc_trace(UVC_TRACE_CLOCK, "%s: PTS %u y %llu.%06llu SOF %u.%06llu "
  		  "(x1 %u x2 %u y1 %u y2 %u SOF offset %u)\n",
  		  stream->dev->name, buf->pts,
  		  y >> 16, div_u64((y & 0xffff) * 1000000, 65536),
  		  sof >> 16, div_u64(((u64)sof & 0xffff) * 1000000LLU, 65536),
  		  x1, x2, y1, y2, clock->sof_offset);
  
  	/* Second step, SOF to host clock conversion. */
  	x1 = (uvc_video_clock_host_sof(first) + 2048) << 16;
  	x2 = (uvc_video_clock_host_sof(last) + 2048) << 16;
  	if (x2 < x1)
  		x2 += 2048 << 16;
  	if (x1 == x2)
  		goto done;
  
  	ts = timespec_sub(last->host_ts, first->host_ts);
  	y1 = NSEC_PER_SEC;
  	y2 = (ts.tv_sec + 1) * NSEC_PER_SEC + ts.tv_nsec;
  
  	/* Interpolated and host SOF timestamps can wrap around at slightly
  	 * different times. Handle this by adding or removing 2048 to or from
  	 * the computed SOF value to keep it close to the SOF samples mean
  	 * value.
  	 */
  	mean = (x1 + x2) / 2;
  	if (mean - (1024 << 16) > sof)
  		sof += 2048 << 16;
  	else if (sof > mean + (1024 << 16))
  		sof -= 2048 << 16;
  
  	y = (u64)(y2 - y1) * (u64)sof + (u64)y1 * (u64)x2
  	  - (u64)y2 * (u64)x1;
  	y = div_u64(y, x2 - x1);
  
  	div = div_u64_rem(y, NSEC_PER_SEC, &rem);
  	ts.tv_sec = first->host_ts.tv_sec - 1 + div;
  	ts.tv_nsec = first->host_ts.tv_nsec + rem;
  	if (ts.tv_nsec >= NSEC_PER_SEC) {
  		ts.tv_sec++;
  		ts.tv_nsec -= NSEC_PER_SEC;
  	}
  
  	uvc_trace(UVC_TRACE_CLOCK, "%s: SOF %u.%06llu y %llu ts %lu.%06lu "
  		  "buf ts %lu.%06lu (x1 %u/%u/%u x2 %u/%u/%u y1 %u y2 %u)\n",
  		  stream->dev->name,
  		  sof >> 16, div_u64(((u64)sof & 0xffff) * 1000000LLU, 65536),
  		  y, ts.tv_sec, ts.tv_nsec / NSEC_PER_USEC,
  		  v4l2_buf->timestamp.tv_sec, v4l2_buf->timestamp.tv_usec,
  		  x1, first->host_sof, first->dev_sof,
  		  x2, last->host_sof, last->dev_sof, y1, y2);
  
  	/* Update the V4L2 buffer. */
  	v4l2_buf->timestamp.tv_sec = ts.tv_sec;
  	v4l2_buf->timestamp.tv_usec = ts.tv_nsec / NSEC_PER_USEC;
  
  done:
  	spin_unlock_irqrestore(&stream->clock.lock, flags);
  }
  
  /* ------------------------------------------------------------------------
   * Stream statistics
   */
  
  static void uvc_video_stats_decode(struct uvc_streaming *stream,
  		const __u8 *data, int len)
  {
  	unsigned int header_size;
  	bool has_pts = false;
  	bool has_scr = false;
  	u16 uninitialized_var(scr_sof);
  	u32 uninitialized_var(scr_stc);
  	u32 uninitialized_var(pts);
  
  	if (stream->stats.stream.nb_frames == 0 &&
  	    stream->stats.frame.nb_packets == 0)
  		ktime_get_ts(&stream->stats.stream.start_ts);
  
  	switch (data[1] & (UVC_STREAM_PTS | UVC_STREAM_SCR)) {
  	case UVC_STREAM_PTS | UVC_STREAM_SCR:
  		header_size = 12;
  		has_pts = true;
  		has_scr = true;
  		break;
  	case UVC_STREAM_PTS:
  		header_size = 6;
  		has_pts = true;
  		break;
  	case UVC_STREAM_SCR:
  		header_size = 8;
  		has_scr = true;
  		break;
  	default:
  		header_size = 2;
  		break;
  	}
  
  	/* Check for invalid headers. */
  	if (len < header_size || data[0] < header_size) {
  		stream->stats.frame.nb_invalid++;
  		return;
  	}
  
  	/* Extract the timestamps. */
  	if (has_pts)
  		pts = get_unaligned_le32(&data[2]);
  
  	if (has_scr) {
  		scr_stc = get_unaligned_le32(&data[header_size - 6]);
  		scr_sof = get_unaligned_le16(&data[header_size - 2]);
  	}
  
  	/* Is PTS constant through the whole frame ? */
  	if (has_pts && stream->stats.frame.nb_pts) {
  		if (stream->stats.frame.pts != pts) {
  			stream->stats.frame.nb_pts_diffs++;
  			stream->stats.frame.last_pts_diff =
  				stream->stats.frame.nb_packets;
  		}
  	}
  
  	if (has_pts) {
  		stream->stats.frame.nb_pts++;
  		stream->stats.frame.pts = pts;
  	}
  
  	/* Do all frames have a PTS in their first non-empty packet, or before
  	 * their first empty packet ?
  	 */
  	if (stream->stats.frame.size == 0) {
  		if (len > header_size)
  			stream->stats.frame.has_initial_pts = has_pts;
  		if (len == header_size && has_pts)
  			stream->stats.frame.has_early_pts = true;
  	}
  
  	/* Do the SCR.STC and SCR.SOF fields vary through the frame ? */
  	if (has_scr && stream->stats.frame.nb_scr) {
  		if (stream->stats.frame.scr_stc != scr_stc)
  			stream->stats.frame.nb_scr_diffs++;
  	}
  
  	if (has_scr) {
  		/* Expand the SOF counter to 32 bits and store its value. */
  		if (stream->stats.stream.nb_frames > 0 ||
  		    stream->stats.frame.nb_scr > 0)
  			stream->stats.stream.scr_sof_count +=
  				(scr_sof - stream->stats.stream.scr_sof) % 2048;
  		stream->stats.stream.scr_sof = scr_sof;
  
  		stream->stats.frame.nb_scr++;
  		stream->stats.frame.scr_stc = scr_stc;
  		stream->stats.frame.scr_sof = scr_sof;
  
  		if (scr_sof < stream->stats.stream.min_sof)
  			stream->stats.stream.min_sof = scr_sof;
  		if (scr_sof > stream->stats.stream.max_sof)
  			stream->stats.stream.max_sof = scr_sof;
  	}
  
  	/* Record the first non-empty packet number. */
  	if (stream->stats.frame.size == 0 && len > header_size)
  		stream->stats.frame.first_data = stream->stats.frame.nb_packets;
  
  	/* Update the frame size. */
  	stream->stats.frame.size += len - header_size;
  
  	/* Update the packets counters. */
  	stream->stats.frame.nb_packets++;
  	if (len > header_size)
  		stream->stats.frame.nb_empty++;
  
  	if (data[1] & UVC_STREAM_ERR)
  		stream->stats.frame.nb_errors++;
  }
  
  static void uvc_video_stats_update(struct uvc_streaming *stream)
  {
  	struct uvc_stats_frame *frame = &stream->stats.frame;
  
  	uvc_trace(UVC_TRACE_STATS, "frame %u stats: %u/%u/%u packets, "
  		  "%u/%u/%u pts (%searly %sinitial), %u/%u scr, "
  		  "last pts/stc/sof %u/%u/%u\n",
  		  stream->sequence, frame->first_data,
  		  frame->nb_packets - frame->nb_empty, frame->nb_packets,
  		  frame->nb_pts_diffs, frame->last_pts_diff, frame->nb_pts,
  		  frame->has_early_pts ? "" : "!",
  		  frame->has_initial_pts ? "" : "!",
  		  frame->nb_scr_diffs, frame->nb_scr,
  		  frame->pts, frame->scr_stc, frame->scr_sof);
  
  	stream->stats.stream.nb_frames++;
  	stream->stats.stream.nb_packets += stream->stats.frame.nb_packets;
  	stream->stats.stream.nb_empty += stream->stats.frame.nb_empty;
  	stream->stats.stream.nb_errors += stream->stats.frame.nb_errors;
  	stream->stats.stream.nb_invalid += stream->stats.frame.nb_invalid;
  
  	if (frame->has_early_pts)
  		stream->stats.stream.nb_pts_early++;
  	if (frame->has_initial_pts)
  		stream->stats.stream.nb_pts_initial++;
  	if (frame->last_pts_diff <= frame->first_data)
  		stream->stats.stream.nb_pts_constant++;
  	if (frame->nb_scr >= frame->nb_packets - frame->nb_empty)
  		stream->stats.stream.nb_scr_count_ok++;
  	if (frame->nb_scr_diffs + 1 == frame->nb_scr)
  		stream->stats.stream.nb_scr_diffs_ok++;
  
  	memset(&stream->stats.frame, 0, sizeof(stream->stats.frame));
  }
  
  size_t uvc_video_stats_dump(struct uvc_streaming *stream, char *buf,
  			    size_t size)
  {
  	unsigned int scr_sof_freq;
  	unsigned int duration;
  	struct timespec ts;
  	size_t count = 0;
  
  	ts.tv_sec = stream->stats.stream.stop_ts.tv_sec
  		  - stream->stats.stream.start_ts.tv_sec;
  	ts.tv_nsec = stream->stats.stream.stop_ts.tv_nsec
  		   - stream->stats.stream.start_ts.tv_nsec;
  	if (ts.tv_nsec < 0) {
  		ts.tv_sec--;
  		ts.tv_nsec += 1000000000;
  	}
  
  	/* Compute the SCR.SOF frequency estimate. At the nominal 1kHz SOF
  	 * frequency this will not overflow before more than 1h.
  	 */
  	duration = ts.tv_sec * 1000 + ts.tv_nsec / 1000000;
  	if (duration != 0)
  		scr_sof_freq = stream->stats.stream.scr_sof_count * 1000
  			     / duration;
  	else
  		scr_sof_freq = 0;
  
  	count += scnprintf(buf + count, size - count,
  			   "frames:  %u\npackets: %u\nempty:   %u\n"
  			   "errors:  %u\ninvalid: %u\n",
  			   stream->stats.stream.nb_frames,
  			   stream->stats.stream.nb_packets,
  			   stream->stats.stream.nb_empty,
  			   stream->stats.stream.nb_errors,
  			   stream->stats.stream.nb_invalid);
  	count += scnprintf(buf + count, size - count,
  			   "pts: %u early, %u initial, %u ok\n",
  			   stream->stats.stream.nb_pts_early,
  			   stream->stats.stream.nb_pts_initial,
  			   stream->stats.stream.nb_pts_constant);
  	count += scnprintf(buf + count, size - count,
  			   "scr: %u count ok, %u diff ok\n",
  			   stream->stats.stream.nb_scr_count_ok,
  			   stream->stats.stream.nb_scr_diffs_ok);
  	count += scnprintf(buf + count, size - count,
  			   "sof: %u <= sof <= %u, freq %u.%03u kHz\n",
  			   stream->stats.stream.min_sof,
  			   stream->stats.stream.max_sof,
  			   scr_sof_freq / 1000, scr_sof_freq % 1000);
  
  	return count;
  }
  
  static void uvc_video_stats_start(struct uvc_streaming *stream)
  {
  	memset(&stream->stats, 0, sizeof(stream->stats));
  	stream->stats.stream.min_sof = 2048;
  }
  
  static void uvc_video_stats_stop(struct uvc_streaming *stream)
  {
  	ktime_get_ts(&stream->stats.stream.stop_ts);
  }
  
  /* ------------------------------------------------------------------------
   * Video codecs
   */
  
  /* Video payload decoding is handled by uvc_video_decode_start(),
   * uvc_video_decode_data() and uvc_video_decode_end().
   *
   * uvc_video_decode_start is called with URB data at the start of a bulk or
   * isochronous payload. It processes header data and returns the header size
   * in bytes if successful. If an error occurs, it returns a negative error
   * code. The following error codes have special meanings.
   *
   * - EAGAIN informs the caller that the current video buffer should be marked
   *   as done, and that the function should be called again with the same data
   *   and a new video buffer. This is used when end of frame conditions can be
   *   reliably detected at the beginning of the next frame only.
   *
   * If an error other than -EAGAIN is returned, the caller will drop the current
   * payload. No call to uvc_video_decode_data and uvc_video_decode_end will be
   * made until the next payload. -ENODATA can be used to drop the current
   * payload if no other error code is appropriate.
   *
   * uvc_video_decode_data is called for every URB with URB data. It copies the
   * data to the video buffer.
   *
   * uvc_video_decode_end is called with header data at the end of a bulk or
   * isochronous payload. It performs any additional header data processing and
   * returns 0 or a negative error code if an error occurred. As header data have
   * already been processed by uvc_video_decode_start, this functions isn't
   * required to perform sanity checks a second time.
   *
   * For isochronous transfers where a payload is always transferred in a single
   * URB, the three functions will be called in a row.
   *
   * To let the decoder process header data and update its internal state even
   * when no video buffer is available, uvc_video_decode_start must be prepared
   * to be called with a NULL buf parameter. uvc_video_decode_data and
   * uvc_video_decode_end will never be called with a NULL buffer.
   */
  static int uvc_video_decode_start(struct uvc_streaming *stream,
  		struct uvc_buffer *buf, const __u8 *data, int len)
  {
  	__u8 fid;
  
  	/* Sanity checks:
  	 * - packet must be at least 2 bytes long
  	 * - bHeaderLength value must be at least 2 bytes (see above)
  	 * - bHeaderLength value can't be larger than the packet size.
  	 */
  	if (len < 2 || data[0] < 2 || data[0] > len) {
  		stream->stats.frame.nb_invalid++;
  		return -EINVAL;
  	}
  
  	fid = data[1] & UVC_STREAM_FID;
  
  	/* Increase the sequence number regardless of any buffer states, so
  	 * that discontinuous sequence numbers always indicate lost frames.
  	 */
  	if (stream->last_fid != fid) {
  		stream->sequence++;
  		if (stream->sequence)
  			uvc_video_stats_update(stream);
  	}
  
  	uvc_video_clock_decode(stream, buf, data, len);
  	uvc_video_stats_decode(stream, data, len);
  
  	/* Store the payload FID bit and return immediately when the buffer is
  	 * NULL.
  	 */
  	if (buf == NULL) {
  		stream->last_fid = fid;
  		return -ENODATA;
  	}
  
  	/* Mark the buffer as bad if the error bit is set. */
  	if (data[1] & UVC_STREAM_ERR) {
  		uvc_trace(UVC_TRACE_FRAME, "Marking buffer as bad (error bit "
  			  "set).\n");
  		buf->error = 1;
  	}
  
  	/* Synchronize to the input stream by waiting for the FID bit to be
  	 * toggled when the the buffer state is not UVC_BUF_STATE_ACTIVE.
  	 * stream->last_fid is initialized to -1, so the first isochronous
  	 * frame will always be in sync.
  	 *
  	 * If the device doesn't toggle the FID bit, invert stream->last_fid
  	 * when the EOF bit is set to force synchronisation on the next packet.
  	 */
  	if (buf->state != UVC_BUF_STATE_ACTIVE) {
  		struct timespec ts;
  
  		if (fid == stream->last_fid) {
  			uvc_trace(UVC_TRACE_FRAME, "Dropping payload (out of "
  				"sync).\n");
  			if ((stream->dev->quirks & UVC_QUIRK_STREAM_NO_FID) &&
  			    (data[1] & UVC_STREAM_EOF))
  				stream->last_fid ^= UVC_STREAM_FID;
  			return -ENODATA;
  		}
  
  		if (uvc_clock_param == CLOCK_MONOTONIC)
  			ktime_get_ts(&ts);
  		else
  			ktime_get_real_ts(&ts);
  
  		buf->buf.v4l2_buf.sequence = stream->sequence;
  		buf->buf.v4l2_buf.timestamp.tv_sec = ts.tv_sec;
  		buf->buf.v4l2_buf.timestamp.tv_usec =
  			ts.tv_nsec / NSEC_PER_USEC;
  
  		/* TODO: Handle PTS and SCR. */
  		buf->state = UVC_BUF_STATE_ACTIVE;
  	}
  
  	/* Mark the buffer as done if we're at the beginning of a new frame.
  	 * End of frame detection is better implemented by checking the EOF
  	 * bit (FID bit toggling is delayed by one frame compared to the EOF
  	 * bit), but some devices don't set the bit at end of frame (and the
  	 * last payload can be lost anyway). We thus must check if the FID has
  	 * been toggled.
  	 *
  	 * stream->last_fid is initialized to -1, so the first isochronous
  	 * frame will never trigger an end of frame detection.
  	 *
  	 * Empty buffers (bytesused == 0) don't trigger end of frame detection
  	 * as it doesn't make sense to return an empty buffer. This also
  	 * avoids detecting end of frame conditions at FID toggling if the
  	 * previous payload had the EOF bit set.
  	 */
  	if (fid != stream->last_fid && buf->bytesused != 0) {
  		uvc_trace(UVC_TRACE_FRAME, "Frame complete (FID bit "
  				"toggled).\n");
  		buf->state = UVC_BUF_STATE_READY;
  		return -EAGAIN;
  	}
  
  	stream->last_fid = fid;
  
  	return data[0];
  }
  
  static void uvc_video_decode_data(struct uvc_streaming *stream,
  		struct uvc_buffer *buf, const __u8 *data, int len)
  {
  	unsigned int maxlen, nbytes;
  	void *mem;
  
  	if (len <= 0)
  		return;
  
  	/* Copy the video data to the buffer. */
  	maxlen = buf->length - buf->bytesused;
  	mem = buf->mem + buf->bytesused;
  	nbytes = min((unsigned int)len, maxlen);
  	memcpy(mem, data, nbytes);
  	buf->bytesused += nbytes;
  
  	/* Complete the current frame if the buffer size was exceeded. */
  	if (len > maxlen) {
  		uvc_trace(UVC_TRACE_FRAME, "Frame complete (overflow).\n");
  		buf->state = UVC_BUF_STATE_READY;
  	}
  }
  
  static void uvc_video_decode_end(struct uvc_streaming *stream,
  		struct uvc_buffer *buf, const __u8 *data, int len)
  {
  	/* Mark the buffer as done if the EOF marker is set. */
  	if (data[1] & UVC_STREAM_EOF && buf->bytesused != 0) {
  		uvc_trace(UVC_TRACE_FRAME, "Frame complete (EOF found).\n");
  		if (data[0] == len)
  			uvc_trace(UVC_TRACE_FRAME, "EOF in empty payload.\n");
  		buf->state = UVC_BUF_STATE_READY;
  		if (stream->dev->quirks & UVC_QUIRK_STREAM_NO_FID)
  			stream->last_fid ^= UVC_STREAM_FID;
  	}
  }
  
  /* Video payload encoding is handled by uvc_video_encode_header() and
   * uvc_video_encode_data(). Only bulk transfers are currently supported.
   *
   * uvc_video_encode_header is called at the start of a payload. It adds header
   * data to the transfer buffer and returns the header size. As the only known
   * UVC output device transfers a whole frame in a single payload, the EOF bit
   * is always set in the header.
   *
   * uvc_video_encode_data is called for every URB and copies the data from the
   * video buffer to the transfer buffer.
   */
  static int uvc_video_encode_header(struct uvc_streaming *stream,
  		struct uvc_buffer *buf, __u8 *data, int len)
  {
  	data[0] = 2;	/* Header length */
  	data[1] = UVC_STREAM_EOH | UVC_STREAM_EOF
  		| (stream->last_fid & UVC_STREAM_FID);
  	return 2;
  }
  
  static int uvc_video_encode_data(struct uvc_streaming *stream,
  		struct uvc_buffer *buf, __u8 *data, int len)
  {
  	struct uvc_video_queue *queue = &stream->queue;
  	unsigned int nbytes;
  	void *mem;
  
  	/* Copy video data to the URB buffer. */
  	mem = buf->mem + queue->buf_used;
  	nbytes = min((unsigned int)len, buf->bytesused - queue->buf_used);
  	nbytes = min(stream->bulk.max_payload_size - stream->bulk.payload_size,
  			nbytes);
  	memcpy(data, mem, nbytes);
  
  	queue->buf_used += nbytes;
  
  	return nbytes;
  }
  
  /* ------------------------------------------------------------------------
   * URB handling
   */
  
  /*
   * Completion handler for video URBs.
   */
  static void uvc_video_decode_isoc(struct urb *urb, struct uvc_streaming *stream,
  	struct uvc_buffer *buf)
  {
  	u8 *mem;
  	int ret, i;
  
  	for (i = 0; i < urb->number_of_packets; ++i) {
  		if (urb->iso_frame_desc[i].status < 0) {
  			uvc_trace(UVC_TRACE_FRAME, "USB isochronous frame "
  				"lost (%d).\n", urb->iso_frame_desc[i].status);
  			/* Mark the buffer as faulty. */
  			if (buf != NULL)
  				buf->error = 1;
  			continue;
  		}
  
  		/* Decode the payload header. */
  		mem = urb->transfer_buffer + urb->iso_frame_desc[i].offset;
  		do {
  			ret = uvc_video_decode_start(stream, buf, mem,
  				urb->iso_frame_desc[i].actual_length);
  			if (ret == -EAGAIN)
  				buf = uvc_queue_next_buffer(&stream->queue,
  							    buf);
  		} while (ret == -EAGAIN);
  
  		if (ret < 0)
  			continue;
  
  		/* Decode the payload data. */
  		uvc_video_decode_data(stream, buf, mem + ret,
  			urb->iso_frame_desc[i].actual_length - ret);
  
  		/* Process the header again. */
  		uvc_video_decode_end(stream, buf, mem,
  			urb->iso_frame_desc[i].actual_length);
  
  		if (buf->state == UVC_BUF_STATE_READY) {
  			if (buf->length != buf->bytesused &&
  			    !(stream->cur_format->flags &
  			      UVC_FMT_FLAG_COMPRESSED))
  				buf->error = 1;
  
  			buf = uvc_queue_next_buffer(&stream->queue, buf);
  		}
  	}
  }
  
  static void uvc_video_decode_bulk(struct urb *urb, struct uvc_streaming *stream,
  	struct uvc_buffer *buf)
  {
  	u8 *mem;
  	int len, ret;
  
  	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;
  
  	uvc_video_clock_reset(stream);
  
  	ret = uvc_commit_video(stream, &stream->ctrl);
  	if (ret < 0) {
  		uvc_queue_enable(&stream->queue, 0);
  		return ret;
  	}
  
  	if (!uvc_queue_streaming(&stream->queue))
  		return 0;
  
  	ret = uvc_init_video(stream, GFP_NOIO);
  	if (ret < 0)
  		uvc_queue_enable(&stream->queue, 0);
  
  	return ret;
  }
  
  /* ------------------------------------------------------------------------
   * Video device
   */
  
  /*
   * Initialize the UVC video device by switching to alternate setting 0 and
   * retrieve the default format.
   *
   * Some cameras (namely the Fuji Finepix) set the format and frame
   * indexes to zero. The UVC standard doesn't clearly make this a spec
   * violation, so try to silently fix the values if possible.
   *
   * This function is called before registering the device with V4L.
   */
  int uvc_video_init(struct uvc_streaming *stream)
  {
  	struct uvc_streaming_control *probe = &stream->ctrl;
  	struct uvc_format *format = NULL;
  	struct uvc_frame *frame = NULL;
  	unsigned int i;
  	int ret;
  
  	if (stream->nformats == 0) {
  		uvc_printk(KERN_INFO, "No supported video formats found.\n");
  		return -EINVAL;
  	}
  
  	atomic_set(&stream->active, 0);
  
  	/* Initialize the video buffers queue. */
  	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);
  		uvc_video_clock_cleanup(stream);
  		return 0;
  	}
  
  	ret = uvc_video_clock_init(stream);
  	if (ret < 0)
  		return ret;
  
  	ret = uvc_queue_enable(&stream->queue, 1);
  	if (ret < 0)
  		goto error_queue;
  
  	/* Commit the streaming parameters. */
  	ret = uvc_commit_video(stream, &stream->ctrl);
  	if (ret < 0)
  		goto error_commit;
  
  	ret = uvc_init_video(stream, GFP_KERNEL);
  	if (ret < 0)
  		goto error_video;
  
  	return 0;
  
  error_video:
  	usb_set_interface(stream->dev->udev, stream->intfnum, 0);
  error_commit:
  	uvc_queue_enable(&stream->queue, 0);
  error_queue:
  	uvc_video_clock_cleanup(stream);
  
  	return ret;
  }
  