linux-kernel - Re: [PATCH v9 17/22] media: docs: Document the behaviour of uvcdriver

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Message-ID: <YMJHDLSoimKCMsB9@pendragon.ideasonboard.com>
Date:   Thu, 10 Jun 2021 20:08:28 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Hans Verkuil <hverkuil-cisco@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tomasz Figa <tfiga@...omium.org>
Subject: Re: [PATCH v9 17/22] media: docs: Document the behaviour of uvcdriver

Hi Ricardo,

Thank you for the patch.

On Sat, Mar 27, 2021 at 01:01:05PM +0100, Ricardo Ribalda wrote:
> On Sat, Mar 27, 2021 at 12:19 PM Hans Verkuil <hverkuil-cisco@...all.nl> wrote:
> > On 26/03/2021 10:58, Ricardo Ribalda wrote:
> > > The uvc driver relies on the camera firmware to keep the control states
> > > and therefore is not capable of changing an inactive control.
> > >
> > > Allow returning -EACESS in those cases.
> >
> > -EACCES
> 
> This british people that like to have a lot of double consonants :)
> 
> I have updated the series at:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/ribalda/linux.git/log/?h=uvc-compliance-v10
> 
> Will not post until there is more feedback to avoid spamming the list.

s/uvcdriver/uvcvideo driver/ in the subject line.

For the version in that branch,

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> > >
> > > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > > ---
> > >  Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst      | 5 +++++
> > >  Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst | 5 +++++
> > >  2 files changed, 10 insertions(+)
> > >
> > > diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst b/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst
> > > index 4f1bed53fad5..8c0a203385c2 100644
> > > --- a/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst
> > > +++ b/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst
> > > @@ -95,3 +95,8 @@ EBUSY
> > >
> > >  EACCES
> > >      Attempt to set a read-only control or to get a write-only control.
> > > +
> > > +    Or if there is an attempt to set an inactive control and the driver is
> > > +    not capable of keeping the new value until the control is active again.
> >
> > keeping: 'caching' or 'storing' are better words, I think.
> >
> > > +    This is the case for drivers that do not use the standard control
> > > +    framework and rely purely on the hardware to keep the controls' state.
> >
> > I would drop that last sentence. It is not relevant information to the users of
> > the API.
> >
> > > diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> > > index b9c62affbb5a..bb7de7a25241 100644
> > > --- a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> > > +++ b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> > > @@ -438,3 +438,8 @@ EACCES
> > >
> > >      Or the ``which`` field was set to ``V4L2_CTRL_WHICH_REQUEST_VAL`` but the
> > >      device does not support requests.
> > > +
> > > +    Or if there is an attempt to set an inactive control and the driver is
> > > +    not capable of keeping the new value until the control is active again.
> > > +    This is the case for drivers that do not use the standard control
> > > +    framework and rely purely on the hardware to keep the controls' state.
> >
> > Same comments as above.

-- 
Regards,

Laurent Pinchart