diff mbox series

[1/2] media: uvcvideo: Fix hw timestamp handling for slow FPS

Message ID 20240610-hwtimestamp-followup-v1-1-f9eaed7be7f0@chromium.org
State New
Headers show
Series media: uvcvideo: Followup hwtimestamp patches | expand

Commit Message

Ricardo Ribalda June 10, 2024, 7:17 p.m. UTC 
In UVC 1.5 we get a single clock value per frame. With the current
buffer size of 32, FPS slowers than 32 might roll-over twice.

The current code cannot handle two roll-over and provide invalid
timestamps.

Revome all the samples from the circular buffer that are more than two
rollovers old, so the algorithm always provides good timestamps.

Note that we are removing values that are more than one second old,
which means that there is enough distance between the two points that
we use for the interpolation to provide good values.

Tested-by: HungNien Chen <hn.chen@sunplusit.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 drivers/media/usb/uvc/uvc_video.c | 23 +++++++++++++++++++++++
 drivers/media/usb/uvc/uvcvideo.h  |  1 +
 2 files changed, 24 insertions(+)

Comments

Laurent Pinchart June 16, 2024, 11:28 p.m. UTC | #1 
Hi Ricardo,

Thank you for the patch.

On Mon, Jun 10, 2024 at 07:17:48PM +0000, Ricardo Ribalda wrote:
> In UVC 1.5 we get a single clock value per frame. With the current
> buffer size of 32, FPS slowers than 32 might roll-over twice.
> 
> The current code cannot handle two roll-over and provide invalid
> timestamps.
> 
> Revome all the samples from the circular buffer that are more than two
> rollovers old, so the algorithm always provides good timestamps.
> 
> Note that we are removing values that are more than one second old,
> which means that there is enough distance between the two points that
> we use for the interpolation to provide good values.
> 
> Tested-by: HungNien Chen <hn.chen@sunplusit.com>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Reviewed-by: Tomasz Figa <tfiga@chromium.org>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> ---
>  drivers/media/usb/uvc/uvc_video.c | 23 +++++++++++++++++++++++
>  drivers/media/usb/uvc/uvcvideo.h  |  1 +
>  2 files changed, 24 insertions(+)
> 
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index 76a375fe47dc..869876afdcce 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -471,8 +471,30 @@ static void uvc_video_clock_add_sample(struct uvc_clock *clock,
>  {
>  	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);
>  
> +	/* Handle SOF overflows. */
> +	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. */
>  	memcpy(&clock->samples[clock->head], sample, sizeof(*sample));
>  	clock->head = (clock->head + 1) % clock->size;
>  	clock->count = min(clock->count + 1, clock->size);
> @@ -605,6 +627,7 @@ 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;
>  }
>  
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index e5b12717016f..f21207debd54 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -501,6 +501,7 @@ struct uvc_streaming {
>  		unsigned int head;
>  		unsigned int count;
>  		unsigned int size;
> +		unsigned int last_sof_overflow;
>  
>  		u16 last_sof;
>  		u16 sof_offset;
>
diff mbox series

Patch

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 76a375fe47dc..869876afdcce 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -471,8 +471,30 @@  static void uvc_video_clock_add_sample(struct uvc_clock *clock,
 {
 	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);
 
+	/* Handle SOF overflows. */
+	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. */
 	memcpy(&clock->samples[clock->head], sample, sizeof(*sample));
 	clock->head = (clock->head + 1) % clock->size;
 	clock->count = min(clock->count + 1, clock->size);
@@ -605,6 +627,7 @@  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;
 }
 
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index e5b12717016f..f21207debd54 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -501,6 +501,7 @@  struct uvc_streaming {
 		unsigned int head;
 		unsigned int count;
 		unsigned int size;
+		unsigned int last_sof_overflow;
 
 		u16 last_sof;
 		u16 sof_offset;