linux-kernel - Re: [PATCH v4 01/10] usb: gadget: uvc: always set interrupt on zero length requests

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Message-ID: <20240813091714.GA19716@pendragon.ideasonboard.com>
Date: Tue, 13 Aug 2024 12:17:14 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Michael Grzeschik <m.grzeschik@...gutronix.de>
Cc: Daniel Scally <dan.scally@...asonboard.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Avichal Rakesh <arakesh@...gle.com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 01/10] usb: gadget: uvc: always set interrupt on zero
 length requests

Hi Michael,

Thank you for the patch.

On Tue, Aug 13, 2024 at 11:09:25AM +0200, Michael Grzeschik wrote:
> Since the uvc gadget is depending on the completion handler to
> properly enqueue new data, we have to ensure that the requeue mechanism
> is always working. To be safe we always create an interrupt
> on zero length requests.

What do you mean "to be safe" ? Either there's an issue, and then the
commit message should describe it, or there's no issue, and this isn't
needed.

> Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>
> 
> ---
> v3 -> v4: -
> v1 -> v3: new patch
> ---
>  drivers/usb/gadget/function/uvc_video.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
> index d41f5f31dadd5..03bff39cd4902 100644
> --- a/drivers/usb/gadget/function/uvc_video.c
> +++ b/drivers/usb/gadget/function/uvc_video.c
> @@ -303,6 +303,7 @@ static int uvcg_video_usb_req_queue(struct uvc_video *video,
>  		 *   between latency and interrupt load.
>  		 */
>  		if (list_empty(&video->req_free) || ureq->last_buf ||
> +				!req->length ||
>  			!(video->req_int_count %
>  			DIV_ROUND_UP(video->uvc_num_requests, 4))) {
>  			video->req_int_count = 0;

-- 
Regards,

Laurent Pinchart