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

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Message-ID: <CANiDSCsikQaCMFKdrKfqYv=NuhCxy2v--QBUPd00c5jAo6OGnQ@mail.gmail.com>
Date:   Sat, 27 Mar 2021 13:01:05 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Hans Verkuil <hverkuil-cisco@...all.nl>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        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 Hans

Thanks for your review!

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.

Thanks :)

>
> >
> > 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,
>
>         Hans



-- 
Ricardo Ribalda