On 04/10/2017 12:21 PM, Mauro Carvalho Chehab wrote:
> Em Wed, 29 Mar 2017 09:56:47 +0200
> Hans Verkuil <hverkuil@xxxxxxxxx> escreveu:
>
>> The documentation for video capture and output devices claims that the video standard
>> ioctls are required. This is not the case, they are only required for PAL/NTSC/SECAM
>> type inputs and outputs. Sensors do not implement this at all and e.g. HDMI inputs
>> implement the DV Timings ioctls.
>>
>> Just drop the mention of 'video standard' ioctls.
>>
>> Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
>
> This is an API change that has the potential of breaking userspace.
>
> In the past, several applications were failing if VIDIOC_ENUMSTD ioctl is
> not implemented. So, I remember we had this discussion before, but I don't
> remember the dirty details anymore.
>
> Yet, looking at the code, it seems that we ended by making VIDIOC_ENUMSTD
> mandatory and implemented at the core. So, V4L2 core will make this
> ioctl available for all drivers. The core implementattion will, however,
> return -ENODATA if the driver doesn't set video_device.tvnorms, indicating
> that standard video timings are not supported.
>
> So, instead of the enclosed patch, the documentation should mention the
> standard ioctls, saying that G_STD/S_STD are optional, and ENUMSTD is
> mandatory.
I don't think so. In v4l2-dev.c ENUMSTD is only enabled if the driver supports
the s_std ioctl:
if (is_vid || is_vbi || is_tch) {
/* ioctls valid for video or vbi */
if (ops->vidioc_s_std)
set_bit(_IOC_NR(VIDIOC_ENUMSTD), valid_ioctls);
And in case you are wondering: if you have two inputs, one SDTV and one HDTV, then
you have both s_std and s_dv_timings ioctls and if you switch to the HDTV input,
then tvnorms is set to 0, causing ENUMSTD to return -ENODATA. If you switch back,
then the driver will fill in tvnorms to something non-0.
Regards,
Hans
>
> We could include a note about it may return -ENODATA, although the ENUMSTD
> documentation already states that it returns -ENODATA:
> https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/vidioc-enumstd.html
>
> Regards,
> Mauro
>
>> ---
>> diff --git a/Documentation/media/uapi/v4l/dev-capture.rst b/Documentation/media/uapi/v4l/dev-capture.rst
>> index 32b32055d070..4218742ab5d9 100644
>> --- a/Documentation/media/uapi/v4l/dev-capture.rst
>> +++ b/Documentation/media/uapi/v4l/dev-capture.rst
>> @@ -42,8 +42,8 @@ Video capture devices shall support :ref:`audio input <audio>`,
>> :ref:`tuner`, :ref:`controls <control>`,
>> :ref:`cropping and scaling <crop>` and
>> :ref:`streaming parameter <streaming-par>` ioctls as needed. The
>> -:ref:`video input <video>` and :ref:`video standard <standard>`
>> -ioctls must be supported by all video capture devices.
>> +:ref:`video input <video>` ioctls must be supported by all video
>> +capture devices.
>>
>>
>> Image Format Negotiation
>> diff --git a/Documentation/media/uapi/v4l/dev-output.rst b/Documentation/media/uapi/v4l/dev-output.rst
>> index 25ae8ec96fdf..342eb4931f5c 100644
>> --- a/Documentation/media/uapi/v4l/dev-output.rst
>> +++ b/Documentation/media/uapi/v4l/dev-output.rst
>> @@ -40,8 +40,8 @@ Video output devices shall support :ref:`audio output <audio>`,
>> :ref:`modulator <tuner>`, :ref:`controls <control>`,
>> :ref:`cropping and scaling <crop>` and
>> :ref:`streaming parameter <streaming-par>` ioctls as needed. The
>> -:ref:`video output <video>` and :ref:`video standard <standard>`
>> -ioctls must be supported by all video output devices.
>> +:ref:`video output <video>` ioctls must be supported by all video
>> +output devices.
>>
>>
>> Image Format Negotiation
>
>
>
> Thanks,
> Mauro
>
