linux-kernel - Re: [PATCH v4 06/10] usb: gadget: uvc: set req_size once when the vb2 queue is calculated

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Message-ID: <20240813094110.GE19716@pendragon.ideasonboard.com>
Date: Tue, 13 Aug 2024 12:41:10 +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 06/10] usb: gadget: uvc: set req_size once when the
 vb2 queue is calculated

On Tue, Aug 13, 2024 at 11:09:30AM +0200, Michael Grzeschik wrote:
> The uvc gadget driver is calculating the req_size on every
> video_enable/alloc_request and is based on the fixed configfs parameters
> maxpacket, maxburst and mult.
> 
> As those parameters can not be changed once the gadget is started and
> the same calculation is done already early on the
> vb2_streamon/queue_setup path its save to remove one extra calculation
> and reuse the calculation from uvc_queue_setup for the allocation step.

Avoiding double calculations is good, but then don't compute the value
in uvc_queue_setup(). That will also be called multiple times, and its
timing will be controlled by userspace. Move it to a better location.

> Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>
> 
> ---
> v3 -> v4: -
> v2 -> v3: -
> v1 -> v2: -
> ---
>  drivers/usb/gadget/function/uvc_queue.c |  2 ++
>  drivers/usb/gadget/function/uvc_video.c | 15 ++-------------
>  2 files changed, 4 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/usb/gadget/function/uvc_queue.c b/drivers/usb/gadget/function/uvc_queue.c
> index 7995dd3fef184..2414d78b031f4 100644
> --- a/drivers/usb/gadget/function/uvc_queue.c
> +++ b/drivers/usb/gadget/function/uvc_queue.c
> @@ -63,6 +63,8 @@ static int uvc_queue_setup(struct vb2_queue *vq,
>  	 */
>  	nreq = DIV_ROUND_UP(DIV_ROUND_UP(sizes[0], 2), req_size);
>  	nreq = clamp(nreq, 4U, 64U);
> +
> +	video->req_size = req_size;
>  	video->uvc_num_requests = nreq;
>  
>  	return 0;
> diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
> index 259920ae36843..a6786beef91ad 100644
> --- a/drivers/usb/gadget/function/uvc_video.c
> +++ b/drivers/usb/gadget/function/uvc_video.c
> @@ -480,7 +480,6 @@ uvc_video_free_requests(struct uvc_video *video)
>  	INIT_LIST_HEAD(&video->ureqs);
>  	INIT_LIST_HEAD(&video->req_free);
>  	INIT_LIST_HEAD(&video->req_ready);
> -	video->req_size = 0;
>  	return 0;
>  }
>  
> @@ -488,16 +487,9 @@ static int
>  uvc_video_alloc_requests(struct uvc_video *video)
>  {
>  	struct uvc_request *ureq;
> -	unsigned int req_size;
>  	unsigned int i;
>  	int ret = -ENOMEM;
>  
> -	BUG_ON(video->req_size);
> -
> -	req_size = video->ep->maxpacket
> -		 * max_t(unsigned int, video->ep->maxburst, 1)
> -		 * (video->ep->mult);
> -
>  	for (i = 0; i < video->uvc_num_requests; i++) {
>  		ureq = kzalloc(sizeof(struct uvc_request), GFP_KERNEL);
>  		if (ureq == NULL)
> @@ -507,7 +499,7 @@ uvc_video_alloc_requests(struct uvc_video *video)
>  
>  		list_add_tail(&ureq->list, &video->ureqs);
>  
> -		ureq->req_buffer = kmalloc(req_size, GFP_KERNEL);
> +		ureq->req_buffer = kmalloc(video->req_size, GFP_KERNEL);
>  		if (ureq->req_buffer == NULL)
>  			goto error;
>  
> @@ -525,12 +517,10 @@ uvc_video_alloc_requests(struct uvc_video *video)
>  		list_add_tail(&ureq->req->list, &video->req_free);
>  		/* req_size/PAGE_SIZE + 1 for overruns and + 1 for header */
>  		sg_alloc_table(&ureq->sgt,
> -			       DIV_ROUND_UP(req_size - UVCG_REQUEST_HEADER_LEN,
> +			       DIV_ROUND_UP(video->req_size - UVCG_REQUEST_HEADER_LEN,
>  					    PAGE_SIZE) + 2, GFP_KERNEL);
>  	}
>  
> -	video->req_size = req_size;
> -
>  	return 0;
>  
>  error:
> @@ -663,7 +653,6 @@ uvcg_video_disable(struct uvc_video *video)
>  	INIT_LIST_HEAD(&video->ureqs);
>  	INIT_LIST_HEAD(&video->req_free);
>  	INIT_LIST_HEAD(&video->req_ready);
> -	video->req_size = 0;
>  	spin_unlock_irqrestore(&video->req_lock, flags);
>  
>  	/*

-- 
Regards,

Laurent Pinchart