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

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Date:   Sat, 27 Mar 2021 13:03:36 +0100
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Ricardo Ribalda <ribalda@...omium.org>
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

On 27/03/2021 13:01, Ricardo Ribalda wrote:
> 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

For v10:

Reviewed-by: Hans Verkuil <hverkuil-cisco@...all.nl>

Thanks!

	Hans

> 
> 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
> 
> 
>