linux-kernel - Re: [PATCH v9 12/22] media: uvcvideo: Increase the size of UVC_METADATA_BUF

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Date:   Thu, 10 Jun 2021 19:48:38 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        tfiga@...omium.org
Subject: Re: [PATCH v9 12/22] media: uvcvideo: Increase the size of
 UVC_METADATA_BUF_SIZE

Hi Ricardo,

Thank you for the patch.

On Fri, Mar 26, 2021 at 10:58:30AM +0100, Ricardo Ribalda wrote:
> Hans has discovered that in his test device, for the H264 format
> bytesused goes up to about 570, for YUYV it will actually go up
> to a bit over 5000 bytes, and for MJPG up to about 2706 bytes.
> 
> We should also, according to V4L2_META_FMT_UVC docs, drop headers when
> the buffer is full.
> 
> Credit-to: Hans Verkuil <hverkuil@...all.nl>
> Reviewed-by: Hans Verkuil <hverkuil-cisco@...all.nl>
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_video.c | 8 +++++---
>  drivers/media/usb/uvc/uvcvideo.h  | 2 +-
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index 25fd8aa23529..ea2903dc3252 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1244,11 +1244,13 @@ static void uvc_video_decode_meta(struct uvc_streaming *stream,
>  	if (!meta_buf || length == 2)
>  		return;
>  
> +	/*
> +	 * According to V4L2_META_FMT_UVC docs, we should drop headers when
> +	 * the buffer is full.
> +	 */
>  	if (meta_buf->length - meta_buf->bytesused <
> -	    length + sizeof(meta->ns) + sizeof(meta->sof)) {
> -		meta_buf->error = 1;

Shouldn't you still set meta_buf->error to 1, even if you drop headers ?
Otherwise the application can't tell if headers have been dropped.

With this fixed,

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> +	    length + sizeof(meta->ns) + sizeof(meta->sof))
>  		return;
> -	}
>  
>  	has_pts = mem[1] & UVC_STREAM_PTS;
>  	has_scr = mem[1] & UVC_STREAM_SCR;
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index b81d3f65e52e..a26bbec8d37b 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -527,7 +527,7 @@ struct uvc_stats_stream {
>  	unsigned int max_sof;		/* Maximum STC.SOF value */
>  };
>  
> -#define UVC_METADATA_BUF_SIZE 1024
> +#define UVC_METADATA_BUF_SIZE 10240
>  
>  /**
>   * struct uvc_copy_op: Context structure to schedule asynchronous memcpy

-- 
Regards,

Laurent Pinchart