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SubjectRe: [PATCH] media: vidioc-queryctrl.rst: clarify combining READ_ONLY with WRITE_ONLY
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Hi Hans

On 9/25/19 12:17 PM, Hans Verkuil wrote:
> On 9/25/19 5:09 PM, Helen Koike wrote:
>> Make it clear in the documentation that V4L2_CTRL_FLAG_READ_ONLY doesn't
>> conflict with V4L2_CTRL_FLAG_WRITE_ONLY. Also make it clear that
>> if both are combined then the control has read and write permissions.
>
> That doesn't look right.
>
> This is the test in v4l2-compliance:
>
> __u32 rw_mask = V4L2_CTRL_FLAG_READ_ONLY | V4L2_CTRL_FLAG_WRITE_ONLY;
>
> if ((fl & rw_mask) == rw_mask)
> return fail("can't read nor write this control\n");
>
> If both flags are set, then a fail is reported.
>
> Did you mis-read?
>
> Setting both flags makes no sense.

Maybe I misunderstood the V4L2_CTRL_TYPE_CTRL_CLASS, from v4l2-compliance:

case V4L2_CTRL_TYPE_CTRL_CLASS:
if (fl != (V4L2_CTRL_FLAG_READ_ONLY | V4L2_CTRL_FLAG_WRITE_ONLY))
return fail("invalid flags for control class\n");

I was confused why vivid was using both flags in vivid_ctrl_class (and also the debayer patch that was following this model).

Why both flags are expected when this type is used?

Thanks,
Helen

>
> Regards,
>
> Hans
>
>>
>> Signed-off-by: Helen Koike <helen.koike@collabora.com>
>>
>> ---
>> Hi,
>>
>> v4l2-compliance expects both flags for read and write permissions, so I
>> would like to make it clear in the docs.
>> Please let me know if this is not the case.
>>
>> Thanks
>> Helen
>> ---
>> Documentation/media/uapi/v4l/vidioc-queryctrl.rst | 10 ++++++++++
>> 1 file changed, 10 insertions(+)
>>
>> diff --git a/Documentation/media/uapi/v4l/vidioc-queryctrl.rst b/Documentation/media/uapi/v4l/vidioc-queryctrl.rst
>> index a3d56ffbf4cc..1d3aecdf679f 100644
>> --- a/Documentation/media/uapi/v4l/vidioc-queryctrl.rst
>> +++ b/Documentation/media/uapi/v4l/vidioc-queryctrl.rst
>> @@ -500,6 +500,11 @@ See also the examples in :ref:`control`.
>> - 0x0004
>> - This control is permanently readable only. Any attempt to change
>> the control will result in an ``EINVAL`` error code.
>> +
>> + .. note::
>> +
>> + If combined with ``V4L2_CTRL_FLAG_WRITE_ONLY``, then both, read
>> + and write are allowed.
>> * - ``V4L2_CTRL_FLAG_UPDATE``
>> - 0x0008
>> - A hint that changing this control may affect the value of other
>> @@ -523,6 +528,11 @@ See also the examples in :ref:`control`.
>> where writing a value will cause the device to carry out a given
>> action (e. g. motor control) but no meaningful value can be
>> returned.
>> +
>> + .. note::
>> +
>> + If combined with ``V4L2_CTRL_FLAG_READ_ONLY``, then both, read
>> + and write are allowed.
>> * - ``V4L2_CTRL_FLAG_VOLATILE``
>> - 0x0080
>> - This control is volatile, which means that the value of the
>>
>

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