Re: [PATCH] uvc: gadget: uvc: Defer uvcg_complete_buffer() until .complete()

[Michael Grzeschik <mgr@pengutronix.de>]

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On Mon, Oct 03, 2022 at 11:16:27AM +0100, Daniel Scally wrote:
>Calling uvcg_complete_buffer() from uvc_video_encode_isoc() sometimes
>causes the final isoc packet for a video frame to be delayed long
>enough to cause the USB controller to drop it. The first isoc packet
>of the next video frame is then received by the host, which interprets
>the toggled FID bit correctly such that the stream continues without
>interruption, but the first frame will be missing the last isoc
>packet's worth of bytes.
>
>To fix the issue delay the call to uvcg_complete_buffer() until the
>usb_request's .complete() callback, as already happens when the data
>is encoded via uvc_video_encode_isoc_sg().
>
>Signed-off-by: Daniel Scally <dan.scally@ideasonboard.com>
>---
> drivers/usb/gadget/function/uvc_video.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
>index c00ce0e91f5d..041819a655ed 100644
>--- a/drivers/usb/gadget/function/uvc_video.c
>+++ b/drivers/usb/gadget/function/uvc_video.c
>@@ -194,6 +194,7 @@ static void
> uvc_video_encode_isoc(struct usb_request *req, struct uvc_video *video,
> 		struct uvc_buffer *buf)
> {
>+	struct uvc_request *ureq = req->context;
> 	void *mem = req->buf;
> 	int len = video->req_size;
> 	int ret;
>@@ -213,7 +214,7 @@ uvc_video_encode_isoc(struct usb_request *req, struct uvc_video *video,
> 		video->queue.buf_used = 0;
> 		buf->state = UVC_BUF_STATE_DONE;
> 		list_del(&buf->queue);
>-		uvcg_complete_buffer(&video->queue, buf);
>+		ureq->last_buf = buf;
> 		video->fid ^= UVC_STREAM_FID;
> 	}
> }
>-- 
>2.34.1

Reviewed-by: Michael Grzeschik <m.grzeschik@pengutronix.de>

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