linux-kernel - Re: [PATCH v6 5/5] media: uvcvideo: Do not turn on the camera for some ioctls

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Message-ID: <CANiDSCvM_V0Pv+cxd31AwcXjG-etJ3imsDYfRb7W2t0NKT67OA@mail.gmail.com>
Date: Fri, 9 May 2025 15:51:46 +0200
From: Ricardo Ribalda <ribalda@...omium.org>
To: Hans Verkuil <hans@...erkuil.nl>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>, Hans de Goede <hdegoede@...hat.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, 
	Guennadi Liakhovetski <guennadi.liakhovetski@...el.com>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Subject: Re: [PATCH v6 5/5] media: uvcvideo: Do not turn on the camera for
 some ioctls

Hi Hans

On Fri, 9 May 2025 at 15:44, Hans Verkuil <hans@...erkuil.nl> wrote:
>
> On 27/03/2025 22:05, Ricardo Ribalda wrote:
> > There are some ioctls that do not need to turn on the camera. Do not
> > call uvc_pm_get in those cases.
> >
> > Reviewed-by: Hans de Goede <hdegoede@...hat.com>
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> >  drivers/media/usb/uvc/uvc_v4l2.c | 20 ++++++++++++++++++++
> >  1 file changed, 20 insertions(+)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> > index 0f1ed0387b2611c8d21e211afe21a35101071d93..668a4e9d772c6d91f045ca75e2744b3a6c69da6b 100644
> > --- a/drivers/media/usb/uvc/uvc_v4l2.c
> > +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> > @@ -1440,6 +1440,26 @@ static long uvc_v4l2_unlocked_ioctl(struct file *file,
> >       struct uvc_fh *handle = file->private_data;
> >       int ret;
> >
> > +     /* The following IOCTLs do not need to turn on the camera. */
> > +     switch (cmd) {
> > +     case VIDIOC_CREATE_BUFS:
> > +     case VIDIOC_DQBUF:
> > +     case VIDIOC_ENUM_FMT:
> > +     case VIDIOC_ENUM_FRAMEINTERVALS:
> > +     case VIDIOC_ENUM_FRAMESIZES:
> > +     case VIDIOC_ENUMINPUT:
> > +     case VIDIOC_EXPBUF:
> > +     case VIDIOC_G_FMT:
> > +     case VIDIOC_G_PARM:
> > +     case VIDIOC_G_SELECTION:
> > +     case VIDIOC_QBUF:
> > +     case VIDIOC_QUERYCAP:
> > +     case VIDIOC_REQBUFS:
> > +     case VIDIOC_SUBSCRIBE_EVENT:
> > +     case VIDIOC_UNSUBSCRIBE_EVENT:
>
> Wouldn't it be better to check against the ioctls that DO need to turn on the camera?

I thought it was safer this way. I will look into inverting the logic
in a follow-up patch.

Regards!

>
> That is more future proof IMHO.
>
> If a new ioctl is created, and uvc implements it and that needs to turn on the camera,
> then presumably you will realize that when you add that ioctl in uvc.
>
> If a new ioctl is created and uvc does not need to turn on the camera, then you will
> almost certainly forget to add it to this list.
>
> I'm not blocking this patch, but I think it will be hard to keep this list up to date.
> Inverting the test is probably much easier to handle in the future.
>
> Apologies if this has been discussed before, if so, just point to that discussion so I
> can read through it.
>
> Regards,
>
>         Hans
>
> > +             return video_ioctl2(file, cmd, arg);
> > +     }
> > +
> >       ret = uvc_pm_get(handle->stream->dev);
> >       if (ret)
> >               return ret;
> >
>


-- 
Ricardo Ribalda