kmssink: add drm-fd property

Submitted by Matteo Valdina @mvaldina

Link to original bug (#795023)

Description

Created attachment 370572
patch for drm-fd property

When I try to use two different pipelines (two different src, two different kmssink, and two different displays) but one single DRM device (in my case an i915) it fails because the device was in use by the first pipeline (single process).

I added the ability to get/set the DRM device FD in kmssink. This solved my scenario.

I think that passing or get the FD could be handy in other scenarios where you want to open the device earlier or you need to do something on the DRM device.

I tested this patch on 1.14 branch and a simple application that start two pipelines in the same process for each output display.

When the first pipeline is in the running state I get the DRM FD and set DRM FD on the second pipeline.

Best
Matteo Valdina

Patch 370572, "patch for drm-fd property":
0001-kmssink-add-drm-fd-property.patch