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

[Mauro Carvalho Chehab <mchehab+samsung@kernel.org>]

Em Fri, 29 Jun 2018 12:26:20 +0200
Hans Verkuil <hverkuil@xs4all.nl> escreveu:

> On 06/29/18 12:06, Mauro Carvalho Chehab wrote:
> > Em Thu, 28 Jun 2018 14:47:05 +0200
> > Hans Verkuil <hverkuil@xs4all.nl> escreveu:
> >   
> >> On 06/28/18 13:37, Mauro Carvalho Chehab wrote:  
> >>> Em Thu, 17 May 2018 16:30:16 +0200
> >>> Niklas Söderlund         <niklas.soderlund+renesas@ragnatech.se> 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.  
> > 
> > Well, the way it is, this change is disruptive, as, as far as I remember,
> > MC-based devices with tvp5150 already sets STD via the /dev/video device.  
> 
> Really? Which driver? I am not aware of this and I think you are mistaken.
> Remember that we are talking about MC-centric drivers. em28xx is not MC-centric,
> even though it has a media device.

OMAP3. There are some boards out there with tvp5150.

> 
> > 
> > If we're willing to add it, we'll need to be clear when one approach
> > should be taken, and be clear that, if the SUBDEV version is used, the
> > driver should not support the non-subdev option.  
> 
> Of course, but in the case of em28xx the tvp5150 v4l-subdev node is never
> created, so this is not a problem.
> 
> Regards,
> 
> 	Hans
> 
> >   
> >>
> >> 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
> >>>     
> >>  
> > 
> > 
> > 
> > Thanks,
> > Mauro
> >   
> 



Thanks,
Mauro