linux-kernel - Re: [PATCH v11] media: uvcvideo: Fix bandwidth issue for Alcor camera.

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Message-ID: <6d1bd031-cdea-441e-98a3-b1f16dc55d4b@redhat.com>
Date: Sat, 17 May 2025 13:51:57 +0200
From: Hans de Goede <hdegoede@...hat.com>
To: chenchangcheng <ccc194101@....com>, laurent.pinchart@...asonboard.com,
 ribalda@...omium.org
Cc: mchehab@...nel.org, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org, chenchangcheng <chenchangcheng@...inos.cn>
Subject: Re: [PATCH v11] media: uvcvideo: Fix bandwidth issue for Alcor
 camera.

Hi chenchangcheng,

On 15-May-25 13:14, chenchangcheng wrote:
> From: chenchangcheng <chenchangcheng@...inos.cn>
> 
> Some broken device return wrong dwMaxPayloadTransferSize fields
> as follows:
>     [  218.632537] [pid:20427,cpu6,guvcview,8]uvcvideo: Device requested 2752512 B/frame bandwidth.
>     [  218.632598] [pid:20427,cpu6,guvcview,9]uvcvideo: No fast enough alt setting for requested bandwidth.
> 
> When dwMaxPayloadTransferSize is greater than maxpsize,
> it will prevent the camera from starting.
> So use the bandwidth of maxpsize.
> 
> Signed-off-by: chenchangcheng <chenchangcheng@...inos.cn>

Thank you for your patch. Laurent has merged this into the uvc/next branch now, see:

https://gitlab.freedesktop.org/linux-media/users/uvc/-/commits/next/

Regards,

Hans



> ---
>  drivers/media/usb/uvc/uvc_video.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index e3567aeb0007..11769a1832d2 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -262,6 +262,15 @@ static void uvc_fixup_video_ctrl(struct uvc_streaming *stream,
>  
>  		ctrl->dwMaxPayloadTransferSize = bandwidth;
>  	}
> +
> +	if (stream->intf->num_altsetting > 1 &&
> +	    ctrl->dwMaxPayloadTransferSize > stream->maxpsize) {
> +		dev_warn_ratelimited(&stream->intf->dev,
> +				     "UVC non compliance: the max payload transmission size (%u) exceeds the size of the ep max packet (%u). Using the max size.\n",
> +				     ctrl->dwMaxPayloadTransferSize,
> +				     stream->maxpsize);
> +		ctrl->dwMaxPayloadTransferSize = stream->maxpsize;
> +	}
>  }
>  
>  static size_t uvc_video_ctrl_size(struct uvc_streaming *stream)
> 
> base-commit: 9f35e33144ae5377d6a8de86dd3bd4d995c6ac65