From: Ricardo Ribalda Date: Wed, 13 May 2026 11:49:22 +0000 (+0000) Subject: media: uvcvideo: Relax the constrains for interpolating the hw clock X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1719d78f832dda8dd3f09a867ba74e05d6f11308;p=thirdparty%2Fkernel%2Flinux.git media: uvcvideo: Relax the constrains for interpolating the hw clock In the initial version we set the min value to 250msec. Looks like 100msec can also provide a good value. Now that we are at it, add a macro to make it cleaner. Fixes: 6243c83be6ee8 ("media: uvcvideo: Allow hw clock updates with buffers not full") Cc: stable@vger.kernel.org Reviewed-by: Hans de Goede Tested-by: Yunke Cao Signed-off-by: Ricardo Ribalda Link: https://patch.msgid.link/20260513-uvc-hwtimestamp-v3-3-7a64838b0b02@chromium.org Signed-off-by: Hans de Goede Signed-off-by: Hans Verkuil --- diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c index bb3ee942e570..d2e61be35bf6 100644 --- a/drivers/media/usb/uvc/uvc_video.c +++ b/drivers/media/usb/uvc/uvc_video.c @@ -494,6 +494,13 @@ static int uvc_commit_video(struct uvc_streaming *stream, * Clocks and timestamps */ +/* + * The accuracy of the hardware timestamping depends on having enough data to + * interpolate between the different clock domains. This value is sof cycles, + * this is, milliseconds. + */ +#define UVC_MIN_HW_TIMESTAMP_DIFF 100 + static inline ktime_t uvc_video_get_time(void) { if (uvc_clock_param == CLOCK_MONOTONIC) @@ -843,13 +850,13 @@ void uvc_video_clock_update(struct uvc_streaming *stream, * buffer, but RAM is expensive these days, specially the infinitely * big. * - * The value of 1/4th of a second was determined by running Android's - * CTS on different devices. + * The value of UVC_MIN_HW_TIMESTAMP_DIFF was determined by running + * Android's CTS on different devices. * - * dev_sof runs at 1KHz, and we have a fixed point precision of - * 16 bits. + * y1 and y2 are dev_sof with a fixed point precision of 16 bits. */ - if (clock->size != clock->count && (y2 - y1) < ((1000 / 4) << 16)) + if (clock->size != clock->count && + (y2 - y1) < (UVC_MIN_HW_TIMESTAMP_DIFF << 16)) goto done; y = (u64)(y2 - y1) * (1ULL << 31) + (u64)y1 * (u64)x2