linux-kernel - Re: [PATCH v4 07/10] usb: gadget: uvc: add g_parm and s

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Message-ID: <Zrs1HhLLkun6_0jD@pengutronix.de>
Date: Tue, 13 Aug 2024 12:27:42 +0200
From: Michael Grzeschik <mgr@...gutronix.de>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
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 07/10] usb: gadget: uvc: add g_parm and s_parm for
 frame interval

On Tue, Aug 13, 2024 at 12:28:20PM +0300, Laurent Pinchart wrote:
>On Tue, Aug 13, 2024 at 12:22:55PM +0300, Laurent Pinchart wrote:
>> On Tue, Aug 13, 2024 at 11:09:31AM +0200, Michael Grzeschik wrote:
>> > The uvc gadget driver is lacking the information which frame interval
>> > was set by the host. We add this information by implementing the g_parm
>> > and s_parm callbacks.
>>
>> As I've said countless times, this kind of hack is not the right way to
>> pass information that the kernel has no use for between two userspace
>> components. Please stop butchering this driver.
>
>Reading further patches in the series I see that you would like to get
>more precise bandwidth information from userspace. That is fine, but I
>don't think s_parm is the right option. This is not a regular V4L2
>driver, pass it the exat information it needs instead, through a
>dedicated API that will provide all the needed data.

We have an API, where we can handover the framerate. Why invent
something new. All we need to fix is also patch you uvc-gadget
implementation.

What other API do you suggest then? Come up with something super new and
special, only dedicated for UVC then?

Regards,
Michael

>> > Signed-off-by: Michael Grzeschik <m.grzeschik@...gutronix.de>
>> > ---
>> > v3 -> v4: -
>> > v2 -> v3: -
>> > v1 -> v2: -
>> > ---
>> >  drivers/usb/gadget/function/uvc.h      |  1 +
>> >  drivers/usb/gadget/function/uvc_v4l2.c | 52 ++++++++++++++++++++++++++++++++++
>> >  2 files changed, 53 insertions(+)
>> >
>> > diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
>> > index b3a5165ac70ec..f6bc58fb02b84 100644
>> > --- a/drivers/usb/gadget/function/uvc.h
>> > +++ b/drivers/usb/gadget/function/uvc.h
>> > @@ -100,6 +100,7 @@ struct uvc_video {
>> >  	unsigned int width;
>> >  	unsigned int height;
>> >  	unsigned int imagesize;
>> > +	unsigned int interval;
>> >  	struct mutex mutex;	/* protects frame parameters */
>> >
>> >  	unsigned int uvc_num_requests;
>> > diff --git a/drivers/usb/gadget/function/uvc_v4l2.c b/drivers/usb/gadget/function/uvc_v4l2.c
>> > index de41519ce9aa0..392fb400aad14 100644
>> > --- a/drivers/usb/gadget/function/uvc_v4l2.c
>> > +++ b/drivers/usb/gadget/function/uvc_v4l2.c
>> > @@ -307,6 +307,56 @@ uvc_v4l2_set_format(struct file *file, void *fh, struct v4l2_format *fmt)
>> >  	return ret;
>> >  }
>> >
>> > +static int uvc_v4l2_g_parm(struct file *file, void *fh,
>> > +			    struct v4l2_streamparm *parm)
>> > +{
>> > +	struct video_device *vdev = video_devdata(file);
>> > +	struct uvc_device *uvc = video_get_drvdata(vdev);
>> > +	struct uvc_video *video = &uvc->video;
>> > +	struct v4l2_fract timeperframe;
>> > +
>> > +	if (parm->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
>> > +		return -EINVAL;
>> > +
>> > +	/* Return the actual frame period. */
>> > +	timeperframe.numerator = video->interval;
>> > +	timeperframe.denominator = 10000000;
>> > +	v4l2_simplify_fraction(&timeperframe.numerator,
>> > +		&timeperframe.denominator, 8, 333);
>> > +
>> > +	uvcg_dbg(&uvc->func, "Getting frame interval of %u/%u (%u)\n",
>> > +		timeperframe.numerator, timeperframe.denominator,
>> > +		video->interval);
>> > +
>> > +	parm->parm.output.timeperframe = timeperframe;
>> > +	parm->parm.output.capability = V4L2_CAP_TIMEPERFRAME;
>> > +
>> > +	return 0;
>> > +}
>> > +
>> > +static int uvc_v4l2_s_parm(struct file *file, void *fh,
>> > +			    struct v4l2_streamparm *parm)
>> > +{
>> > +	struct video_device *vdev = video_devdata(file);
>> > +	struct uvc_device *uvc = video_get_drvdata(vdev);
>> > +	struct uvc_video *video = &uvc->video;
>> > +	struct v4l2_fract timeperframe;
>> > +
>> > +	if (parm->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
>> > +		return -EINVAL;
>> > +
>> > +	timeperframe = parm->parm.output.timeperframe;
>> > +
>> > +	video->interval = v4l2_fraction_to_interval(timeperframe.numerator,
>> > +		timeperframe.denominator);
>> > +
>> > +	uvcg_dbg(&uvc->func, "Setting frame interval to %u/%u (%u)\n",
>> > +		timeperframe.numerator, timeperframe.denominator,
>> > +		video->interval);
>> > +
>> > +	return 0;
>> > +}
>> > +
>> >  static int
>> >  uvc_v4l2_enum_frameintervals(struct file *file, void *fh,
>> >  		struct v4l2_frmivalenum *fival)
>> > @@ -577,6 +627,8 @@ const struct v4l2_ioctl_ops uvc_v4l2_ioctl_ops = {
>> >  	.vidioc_dqbuf = uvc_v4l2_dqbuf,
>> >  	.vidioc_streamon = uvc_v4l2_streamon,
>> >  	.vidioc_streamoff = uvc_v4l2_streamoff,
>> > +	.vidioc_s_parm = uvc_v4l2_s_parm,
>> > +	.vidioc_g_parm = uvc_v4l2_g_parm,
>> >  	.vidioc_subscribe_event = uvc_v4l2_subscribe_event,
>> >  	.vidioc_unsubscribe_event = uvc_v4l2_unsubscribe_event,
>> >  	.vidioc_default = uvc_v4l2_ioctl_default,
>
>-- 
>Regards,
>
>Laurent Pinchart
>

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