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

[Michael Grzeschik]

On Tue, Aug 13, 2024 at 12:41:10PM +0300, Laurent Pinchart wrote:
> 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.

I think I was unclear regarding the avoidance of double calculations.

Actually this is the right place to calculate this, since the
resulting req_size will be dependent on the expected imagesize
and the frameduration, we have to calculate it in every queue_setup.

Since this patch is an preperation for the next change, I will leave the
codebase as is but will add the details in the patch description.

Michael

> > Signed-off-by: Michael Grzeschik <m.grzeschik@xxxxxxxxxxxxxx>
> >
> > ---
> > 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

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