[libcamera-devel] [PATCH 0/3] libcamera: Add new Camera devices property

[Laurent Pinchart]

On Wed, Apr 19, 2023 at 01:11:39PM +0100, Kieran Bingham via libcamera-devel wrote:
> On 19/04/2023 10:45, Jacopo Mondi wrote:
> > On Wed, Apr 19, 2023 at 09:58:18AM +0100, Kieran Bingham via libcamera-devel wrote:
> >> It can be beneficial to allow reporting the devices used by a camera to
> >> facilitate de-duplication of resources when handling cameras from a
> >> centralised infrastructure such as PipeWire.
> > 
> > This series allows to retrieve the list of dev_t a libcamera::Camera
> > handles by using a camera properties.
> > 
> > The CameraManager class however maintains a camerasByDevnum_ map that
> > associates a dev_t with the Camera it is owned by. It would be trivial
> > to reverse the map. Have you considered that ? Getting dev_t from the
> > manager seems more natural than doing so from the Camera (and would
> > avoid the additional template specialization for dev_t you don't like)
> 
> No I haven't, so that's an interesting point. I'll take a look.
> 
> Robert/Wim,
> 
> Do you have any specific requirements here? Do you need to be able to 
> map which devices are used by each camera? Or is a single list sufficient?
> 
> Or maybe returning a map of camera (id?) to device list is best all round?
> 
> My only thought on the separation is the list would have to be 
> re-obtained for hotplugged cameras, while it's available at the 'camera' 
> when on the object. Conversely, perhaps hotplug is a reason to 
> centralize the whole list as after a camera is removed it would need to 
> be updated anyway.
> 
> So - I'll see if I can add in a call on the Camera Manager that returns 
> a map of camera id / dev_t.

The map we expose through the CameraManager is meant for the V4L2
adaptation layer only. I'm actually thinking about how we could avoid
exposing it in the public API. A camera property seems a nicer solution
for the problem at hand.

-- 
Regards,

Laurent Pinchart