CHIP-linux-libre/Documentation/devicetree/bindings/video/rockchip-drm.txt

Rockchip DRM master device
================================

The Rockchip DRM master device is a virtual device needed to list all
vop devices or other display interface nodes that comprise the
graphics subsystem.

Required properties:
- compatible: Should be "rockchip,display-subsystem"
- ports: Should contain a list of phandles pointing to display interface port
  of vop devices. vop definitions as defined in
  Documentation/devicetree/bindings/video/rockchip-vop.txt

example:

display-subsystem {
	compatible = "rockchip,display-subsystem";
	ports = <&vopl_out>, <&vopb_out>;
};