linux-kernel - [PATCH v3 1/8] media: uvcvideo: Extend documentation of uvc_video_clock

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Message-Id: <20220920-resend-hwtimestamp-v3-1-db9faee7f47d@chromium.org>
Date:   Wed, 04 Jan 2023 11:45:19 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     linux-kernel@...r.kernel.org, "hn.chen" <hn.chen@...plusit.com>,
        Ricardo Ribalda <ribalda@...omium.org>,
        linux-media@...r.kernel.org
Subject: [PATCH v3 1/8] media: uvcvideo: Extend documentation of
 uvc_video_clock_decode()

Make an explicit reference to UVC 1.5, explaining how the algorithm
supports the different behaviour of UVC 1.1 and 1.5.

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Tested-by: HungNien Chen <hn.chen@...plusit.com>
Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
---
 drivers/media/usb/uvc/uvc_video.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index d2eb9066e4dc..def079c7a6fd 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -516,7 +516,9 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
 
 	/*
 	 * To limit the amount of data, drop SCRs with an SOF identical to the
-	 * previous one.
+	 * previous one. This filtering is also needed to support UVC 1.5, where
+	 * all the data packets of the same frame contains the same SOF. In that
+	 * case only the first one will match the host_sof.
 	 */
 	dev_sof = get_unaligned_le16(&data[header_size - 2]);
 	if (dev_sof == stream->clock.last_sof)

-- 
2.39.0.314.g84b9a713c41-goog-b4-0.11.0-dev-696ae