Re: [PATCH v3 4/4] uvcvideo: add a metadata device node

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Guennadi,

On Friday 30 Dec 2016 11:43:02 Guennadi Liakhovetski wrote:
> Hi Laurent,
> 
> I'd like to discuss extending this patch a bit, preferably as an
> incremental patch.
> 
> First let me confirm my current understanding of the way the UVC driver
> creates its media device topology. Do I understand it correctly, that the
> driver allocates UVC entities (not media controller entities) for all UVC
> units and terminals, but then uses subdevices for all such UVC entities,
> except terminals, i.e. only for UVC units? struct uvc_entity has an
> embedded struct v4l2_subdev object, but it's unused for UVC terminals.
> Instead terminals are associated to video devices, which are then linked
> into the MC topology? Is this my understanding correct?

That's correct, but looking at the code now, I think the driver should use a 
struct media_entity directly instead of a struct v4l2_subdev as it doesn't 
need any of the infrastructure provided by subdevs.

> I have a problem with the current version of this patch, that there is no
> way to associate video device nodes with respepctive metadata nodes. Would
> it be acceptable to use an MC link for this association?

No, links describe data connections.

> Is it allowed for video device MC entities to have source pads additionally
> to their (usually single) sink pad(s) (in case of input video devices)? If
> that would be acceptable, I could create an additional patch to add a source
> pad to output terminal video nodes to link it to metadata nodes.

That's a hack, I don't think it's a good idea.

-- 
Regards,

Laurent Pinchart