Re: [PATCH v2 2/2] v4l: Add support for STD ioctls on subdev nodes

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On 06/28/18 13:37, Mauro Carvalho Chehab wrote:
> Em Thu, 17 May 2018 16:30:16 +0200
> Niklas Söderlund         <niklas.soderlund+renesas@xxxxxxxxxxxx> escreveu:
> 
>> There is no way to control the standard of subdevices which are part of
>> a media device. The ioctls which exists all target video devices
>> explicitly and the idea is that the video device should talk to the
>> subdevice. For subdevices part of a media graph this is not possible and
>> the standard must be controlled on the subdev device directly.
> 
> Why isn't it possible? A media pipeline should have at least a video
> devnode where the standard ioctls will be issued.

Not for an MC-centric device like the r-car or imx. It's why we have v4l-subdev
ioctls for the DV_TIMINGS API, but the corresponding SDTV standards API is
missing.

And in a complex scenario there is nothing preventing you from having multiple
SDTV inputs, some of which need PAL-BG, some SECAM, some NTSC (less likely)
which are all composed together (think security cameras or something like that).

You definitely cannot set the standard from a video device. If nothing else,
it would be completely inconsistent with how HDMI inputs work.

The whole point of MC centric devices is that you *don't* control subdevs
from video nodes.

Regards,

	Hans

> So, I don't see why you would need to explicitly set the standard inside
> a sub-device.
> 
> The way I see, inside a given pipeline, all subdevs should be using the
> same video standard (maybe except for a m2m device with would have some
> coded that would be doing format conversion).
> 
> Am I missing something?
> 
> Thanks,
> Mauro
> 




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