Subdev notification for video device

Subdev notification for video device

[Divneil Rai WADHAWAN]

Hello,

I have a use case, where, I am using subdev configuration to setup video capture.
The pipeline is something like this:

Subdevs: sd_display, sd_capture
Vdev: vcapture

 (0)sd_display(1) -> (0)sd_capture(1)->(0)vcapture

sd_display informs sd_capture of video resolution change and vdev using sd_capture needs to be informed, so, that vdev capture can be stopped.

Here, subdev notification/subscription is missing to/from vdev, in my understanding.
subdev can send notification to v4l2-dev, but not vdev.
Can you help with that? Thanks.

Regards,
Divneil 

Re: Subdev notification for video device

[Hans Verkuil]

On 03/24/2015 12:49 AM, Divneil Rai WADHAWAN wrote:
> Hello,
> 
> I have a use case, where, I am using subdev configuration to setup video capture.
> The pipeline is something like this:
> 
> Subdevs: sd_display, sd_capture
> Vdev: vcapture
> 
>  (0)sd_display(1) -> (0)sd_capture(1)->(0)vcapture
> 
> sd_display informs sd_capture of video resolution change and vdev using sd_capture needs to be informed, so, that vdev capture can be stopped.
> 
> Here, subdev notification/subscription is missing to/from vdev, in my understanding.
> subdev can send notification to v4l2-dev, but not vdev.
> Can you help with that? Thanks.

This is correct. The subdev doesn't and cannot know anything about which video node(s)
need(s) to send out a source change event. The only driver that can is the top-level driver
that knows the topology and can map the event from the sd to the correct video_device.

If your driver uses the media controller, then it should be possible to write a generic
function that would use the topology to discover automatically which video_device nodes
are linked to the sd and propagate the event to those video devices.

Such a generic v4l2_dev notify function doesn't exist today though. Patches are welcome.

If the driver doesn't use the media controller, then the top-level driver should provide
this knowledge in its v4l2_dev notifier function.

Regards,

	Hans