linux-kernel - [PATCH v3] uvc_video: move clock_decode and stats_decode to the end of decode

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Message-Id: <20240221-uvc-host-video-decode-start-v3-1-40e9b9ced97b@pengutronix.de>
Date: Mon, 18 Mar 2024 10:27:28 +0100
From: Michael Grzeschik <m.grzeschik@...gutronix.de>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 kernel@...gutronix.de, Michael Grzeschik <m.grzeschik@...gutronix.de>
Subject: [PATCH v3] uvc_video: move clock_decode and stats_decode to the
 end of decode_start

When the uvc request will get parsed by uvc_video_decode_start it will
leave the function with -EAGAIN to be restarted on the next frame. While
the first wrong parse the statistics will already be updated with
uvc_video_stats_decode.

One value e.g. is the error_count, which therefor will be incremented
twice in case the fid has changed on the way. This patch fixes the
unnecessary extra parsing by moving the decode functions to the
end of decode_start, when it is save to really parse the data.

Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>
---
Changes in v3:
- Moved the clock_decode and stat_decode to end of function as suggested by Ricardo Ribalda
- Link to v2: https://lore.kernel.org/r/20240221-uvc-host-video-decode-start-v2-1-88c6e17e487a@pengutronix.de

Changes in v2:
- Moved the EAGAIN bailout after the sequence handling as mentioned by Ricardo Ribalda
- Link to v1: https://lore.kernel.org/r/20240221-uvc-host-video-decode-start-v1-1-228995925c70@pengutronix.de
---
 drivers/media/usb/uvc/uvc_video.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 7cbf4692bd875..7471bff0ca894 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1078,9 +1078,6 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
 			uvc_video_stats_update(stream);
 	}
 
-	uvc_video_clock_decode(stream, buf, data, len);
-	uvc_video_stats_decode(stream, data, len);
-
 	/*
 	 * Store the payload FID bit and return immediately when the buffer is
 	 * NULL.
@@ -1147,6 +1144,9 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
 		return -EAGAIN;
 	}
 
+	uvc_video_clock_decode(stream, buf, data, len);
+	uvc_video_stats_decode(stream, data, len);
+
 	stream->last_fid = fid;
 
 	return data[0];

---
base-commit: d99e42ce6b8341d3f09e22c6706461ec900fe172
change-id: 20240221-uvc-host-video-decode-start-af53df5924cd

Best regards,
-- 
Michael Grzeschik <m.grzeschik@...gutronix.de>