diff mbox series

[RESEND,v2,6/8] media: uvcvideo: Allow hw clock updates with buffers not full

Message ID 20220920-resend-hwtimestamp-v2-6-0d7978a817cc@chromium.org
State New
Headers
Series uvcvideo: Fixes for hw timestamping |

Commit Message

Ricardo Ribalda Dec. 2, 2022, 5:02 p.m. UTC 
  With UVC 1.5 we get as little as one clock sample per frame. Which means
that it takes 32 frames to move from the software timestamp to the
hardware timestamp method.

This results in abrupt changes in the timestamping after 32 frames (~1
second), resulting in noticeable artifacts when used for encoding.

With this patch we modify the update algorithm to work with whatever
amount of values are available.

Tested-by: HungNien Chen <hn.chen@sunplusit.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 drivers/media/usb/uvc/uvc_video.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Comments

Laurent Pinchart Dec. 30, 2022, 2:37 p.m. UTC | #1 
Hi Ricardo,

Thank you for the patch.

On Fri, Dec 02, 2022 at 06:02:46PM +0100, Ricardo Ribalda wrote:
> With UVC 1.5 we get as little as one clock sample per frame. Which means
> that it takes 32 frames to move from the software timestamp to the
> hardware timestamp method.
> 
> This results in abrupt changes in the timestamping after 32 frames (~1
> second), resulting in noticeable artifacts when used for encoding.
> 
> With this patch we modify the update algorithm to work with whatever
> amount of values are available.

This too makes me thing that we should *really* move this to userspace.
It will but much easier to implement clock domain translation there,
with a better precision.

> Tested-by: HungNien Chen <hn.chen@sunplusit.com>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
>  drivers/media/usb/uvc/uvc_video.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index 75c32e232f5d..7c6448c6d706 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -742,10 +742,10 @@ void uvc_video_clock_update(struct uvc_streaming *stream,
>  
>  	spin_lock_irqsave(&clock->lock, flags);
>  
> -	if (clock->count < clock->size)
> +	if (clock->count < 2)
>  		goto done;
>  
> -	first = &clock->samples[clock->head];
> +	first = &clock->samples[(clock->head - clock->count) % clock->size];
>  	last = &clock->samples[(clock->head - 1) % clock->size];
>  
>  	/* First step, PTS to SOF conversion. */
> @@ -760,6 +760,14 @@ void uvc_video_clock_update(struct uvc_streaming *stream,
>  	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
> +	 * precission.

s/precission/precision/

How did you determine 250ms was the right threshold ?

> +	 */
> +	if ((y2 - y1) < (256 << 16))
> +		goto done;
> +
>  	y = (u64)(y2 - y1) * (1ULL << 31) + (u64)y1 * (u64)x2
>  	  - (u64)y2 * (u64)x1;
>  	y = div_u64(y, x2 - x1);
>
diff mbox series

Patch

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 75c32e232f5d..7c6448c6d706 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -742,10 +742,10 @@  void uvc_video_clock_update(struct uvc_streaming *stream,
 
 	spin_lock_irqsave(&clock->lock, flags);
 
-	if (clock->count < clock->size)
+	if (clock->count < 2)
 		goto done;
 
-	first = &clock->samples[clock->head];
+	first = &clock->samples[(clock->head - clock->count) % clock->size];
 	last = &clock->samples[(clock->head - 1) % clock->size];
 
 	/* First step, PTS to SOF conversion. */
@@ -760,6 +760,14 @@  void uvc_video_clock_update(struct uvc_streaming *stream,
 	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
+	 * precission.
+	 */
+	if ((y2 - y1) < (256 << 16))
+		goto done;
+
 	y = (u64)(y2 - y1) * (1ULL << 31) + (u64)y1 * (u64)x2
 	  - (u64)y2 * (u64)x1;
 	y = div_u64(y, x2 - x1);