From 6243c83be6ee8d95cf5661b5a123621106491974 Mon Sep 17 00:00:00 2001 From: Ricardo Ribalda Date: Sat, 23 Mar 2024 10:48:05 +0000 Subject: [PATCH] media: uvcvideo: Allow hw clock updates with buffers not full 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 Reviewed-by: Sergey Senozhatsky Reviewed-by: Laurent Pinchart Signed-off-by: Ricardo Ribalda Reviewed-by: Tomasz Figa Link: https://lore.kernel.org/r/20240323-resend-hwtimestamp-v10-4-b08e590d97c7@chromium.org Signed-off-by: Laurent Pinchart --- drivers/media/usb/uvc/uvc_video.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c index d6ca383f643e..af25b9f1b53f 100644 --- a/drivers/media/usb/uvc/uvc_video.c +++ b/drivers/media/usb/uvc/uvc_video.c @@ -768,10 +768,10 @@ 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) % clock->size]; last = &clock->samples[(clock->head - 1 + clock->size) % clock->size]; /* First step, PTS to SOF conversion. */ @@ -786,6 +786,18 @@ 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 + * 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); -- 2.25.1