UVC devices transmit a device timestamp along with video frames. Convert
the timestamp to a host timestamp and use it to fill the V4L2 buffer
timestamp field.
Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
---
drivers/media/video/uvc/uvc_queue.c | 12 ++
drivers/media/video/uvc/uvc_video.c | 327 +++++++++++++++++++++++++++++++++++
drivers/media/video/uvc/uvcvideo.h | 25 +++
3 files changed, 364 insertions(+), 0 deletions(-)
diff --git a/drivers/media/video/uvc/uvc_queue.c b/drivers/media/video/uvc/uvc_queue.c
index 268be57..518f77d 100644
--- a/drivers/media/video/uvc/uvc_queue.c
+++ b/drivers/media/video/uvc/uvc_queue.c
@@ -104,10 +104,22 @@ static void uvc_buffer_queue(struct vb2_buffer *vb)
spin_unlock_irqrestore(&queue->irqlock, flags);
}
+static int uvc_buffer_finish(struct vb2_buffer *vb)
+{
+ struct uvc_video_queue *queue = vb2_get_drv_priv(vb->vb2_queue);
+ struct uvc_streaming *stream =
+ container_of(queue, struct uvc_streaming, queue);
+ struct uvc_buffer *buf = container_of(vb, struct uvc_buffer, buf);
+
+ uvc_video_clock_update(stream, &vb->v4l2_buf, buf);
+ return 0;
+}
+
static struct vb2_ops uvc_queue_qops = {
.queue_setup = uvc_queue_setup,
.buf_prepare = uvc_buffer_prepare,
.buf_queue = uvc_buffer_queue,
+ .buf_finish = uvc_buffer_finish,
};
void uvc_queue_init(struct uvc_video_queue *queue, enum v4l2_buf_type type,
diff --git a/drivers/media/video/uvc/uvc_video.c b/drivers/media/video/uvc/uvc_video.c
index 513ba30..d0600a5 100644
--- a/drivers/media/video/uvc/uvc_video.c
+++ b/drivers/media/video/uvc/uvc_video.c
@@ -357,6 +357,326 @@ static int uvc_commit_video(struct uvc_streaming *stream,
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 int uvc_video_clock_init(struct uvc_streaming *stream)
+{
+ struct uvc_clock *clock = &stream->clock;
+
+ spin_lock_init(&clock->lock);
+ clock->head = 0;
+ clock->count = 0;
+ clock->size = 32;
+ clock->last_sof = -1;
+ clock->sof_offset = -1;
+
+ clock->samples = kmalloc(clock->size * sizeof(*clock->samples),
+ GFP_KERNEL);
+ if (clock->samples == NULL)
+ return -ENOMEM;
+
+ 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;
+ 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;
+ 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 = div64_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, div64_u64((y & 0xffff) * 1000000, 65536),
+ sof >> 16, div64_u64(((u64)sof & 0xffff) * 1000000LLU, 65536),
+ x1, x2, y1, y2, clock->sof_offset);
+
+ /* Second step, SOF to host clock conversion. */
+ ts = timespec_sub(last->host_ts, first->host_ts);
+ x1 = (uvc_video_clock_host_sof(first) + 2048) << 16;
+ x2 = (uvc_video_clock_host_sof(last) + 2048) << 16;
+ y1 = NSEC_PER_SEC;
+ y2 = (ts.tv_sec + 1) * NSEC_PER_SEC + ts.tv_nsec;
+
+ if (x2 < x1)
+ x2 += 2048 << 16;
+
+ /* 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 = div64_u64(y, x2 - x1);
+
+ ts.tv_sec = first->host_ts.tv_sec - 1 + y / NSEC_PER_SEC;
+ ts.tv_nsec = first->host_ts.tv_nsec + y % NSEC_PER_SEC;
+ 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, div64_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
*/
@@ -637,6 +957,7 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
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
@@ -1096,6 +1417,8 @@ static void uvc_uninit_video(struct uvc_streaming *stream, int free_buffers)
if (free_buffers)
uvc_free_urb_buffers(stream);
+
+ uvc_video_clock_cleanup(stream);
}
/*
@@ -1225,6 +1548,10 @@ static int uvc_init_video(struct uvc_streaming *stream, gfp_t gfp_flags)
uvc_video_stats_start(stream);
+ ret = uvc_video_clock_init(stream);
+ if (ret < 0)
+ return ret;
+
if (intf->num_altsetting > 1) {
struct usb_host_endpoint *best_ep = NULL;
unsigned int best_psize = 3 * 1024;
diff --git a/drivers/media/video/uvc/uvcvideo.h b/drivers/media/video/uvc/uvcvideo.h
index e4d4b6d..e9c19f5 100644
--- a/drivers/media/video/uvc/uvcvideo.h
+++ b/drivers/media/video/uvc/uvcvideo.h
@@ -329,6 +329,8 @@ struct uvc_buffer {
void *mem;
unsigned int length;
unsigned int bytesused;
+
+ u32 pts;
};
#define UVC_QUEUE_DISCONNECTED (1 << 0)
@@ -455,6 +457,25 @@ struct uvc_streaming {
struct uvc_stats_frame frame;
struct uvc_stats_stream stream;
} stats;
+
+ /* Timestamps support. */
+ struct uvc_clock {
+ struct uvc_clock_sample {
+ u32 dev_stc;
+ u16 dev_sof;
+ struct timespec host_ts;
+ u16 host_sof;
+ } *samples;
+
+ unsigned int head;
+ unsigned int count;
+ unsigned int size;
+
+ u16 last_sof;
+ u16 sof_offset;
+
+ spinlock_t lock;
+ } clock;
};
enum uvc_device_state {
@@ -527,6 +548,7 @@ struct uvc_driver {
#define UVC_TRACE_STATUS (1 << 9)
#define UVC_TRACE_VIDEO (1 << 10)
#define UVC_TRACE_STATS (1 << 11)
+#define UVC_TRACE_CLOCK (1 << 12)
#define UVC_WARN_MINMAX 0
#define UVC_WARN_PROBE_DEF 1
@@ -607,6 +629,9 @@ extern int uvc_probe_video(struct uvc_streaming *stream,
struct uvc_streaming_control *probe);
extern int uvc_query_ctrl(struct uvc_device *dev, __u8 query, __u8 unit,
__u8 intfnum, __u8 cs, void *data, __u16 size);
+void uvc_video_clock_update(struct uvc_streaming *stream,
+ struct v4l2_buffer *v4l2_buf,
+ struct uvc_buffer *buf);
/* Status */
extern int uvc_status_init(struct uvc_device *dev);
--
1.7.3.4
--
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