linux-kernel - Re: [PATCH 2/3] media: uvcvideo: Pass allocation size directly to uvc_alloc_urb

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Message-ID: <20260122014708.GB183118@killaraus>
Date: Thu, 22 Jan 2026 03:47:08 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Hans de Goede <hansg@...nel.org>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Johannes Berg <johannes@...solutions.net>,
	Laurent Pinchart <laurent.pinchart@...net.be>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] media: uvcvideo: Pass allocation size directly to
 uvc_alloc_urb_buffer

Hi Ricardo,

Thank you for the patch.

On Wed, Jan 14, 2026 at 10:32:14AM +0000, Ricardo Ribalda wrote:
> The uvc_alloc_urb_buffer() function implicitly depended on the
> stream->urb_size field, which was set by its caller,
> uvc_alloc_urb_buffers(). This implicit data flow makes the code harder
> to follow.
> 
> More importantly, stream->urb_size was updated within the allocation
> loop before the allocation was confirmed to be successful. If the
> allocation failed, the stream object would be left with a urb_size that
> doesn't correspond to valid, allocated URB buffers.
> 
> Refactor uvc_alloc_urb_buffer() to accept the buffer size as an explicit
> argument. This makes the function's dependencies clear and improves the
> robustness of the error handling path. The stream->urb_size is now set only
> after a complete and successful allocation.
> 
> This is a pure refactoring and introduces no functional changes.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>

It's cleaner indeed.

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

> ---
>  drivers/media/usb/uvc/uvc_video.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index ec76595f3c4be0f49b798ec663d6855d78ab21c4..59eb95a4b70c05b1a12986e908b7e9979b064fd0 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1771,12 +1771,13 @@ static void uvc_free_urb_buffers(struct uvc_streaming *stream)
>  }
>  
>  static bool uvc_alloc_urb_buffer(struct uvc_streaming *stream,
> -				 struct uvc_urb *uvc_urb, gfp_t gfp_flags)
> +				 struct uvc_urb *uvc_urb, unsigned int size,
> +				 gfp_t gfp_flags)
>  {
>  	struct usb_device *udev = stream->dev->udev;
>  
> -	uvc_urb->buffer = usb_alloc_noncoherent(udev, stream->urb_size,
> -						gfp_flags, &uvc_urb->dma,
> +	uvc_urb->buffer = usb_alloc_noncoherent(udev, size, gfp_flags,
> +						&uvc_urb->dma,
>  						uvc_stream_dir(stream),
>  						&uvc_urb->sgt);
>  	return !!uvc_urb->buffer;
> @@ -1813,12 +1814,13 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
>  
>  	/* Retry allocations until one succeed. */
>  	for (; npackets > 0; npackets /= 2) {
> -		stream->urb_size = psize * npackets;
> +		unsigned int urb_size = psize * npackets;
>  
>  		for (i = 0; i < UVC_URBS; ++i) {
>  			struct uvc_urb *uvc_urb = &stream->uvc_urb[i];
>  
> -			if (!uvc_alloc_urb_buffer(stream, uvc_urb, gfp_flags)) {
> +			if (!uvc_alloc_urb_buffer(stream, uvc_urb, urb_size,
> +						  gfp_flags)) {
>  				uvc_free_urb_buffers(stream);
>  				break;
>  			}
> @@ -1830,6 +1832,7 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
>  			uvc_dbg(stream->dev, VIDEO,
>  				"Allocated %u URB buffers of %ux%u bytes each\n",
>  				UVC_URBS, npackets, psize);
> +			stream->urb_size = urb_size;
>  			return npackets;
>  		}
>  	}
> @@ -1837,7 +1840,6 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
>  	uvc_dbg(stream->dev, VIDEO,
>  		"Failed to allocate URB buffers (%u bytes per packet)\n",
>  		psize);
> -	stream->urb_size = 0;
>  	return 0;
>  }
>  

-- 
Regards,

Laurent Pinchart