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/display/rockchip/rockchip-vop.txt

Optional properties
- backlight: spacial backlight required by cabc function.
- secure-memory-region: phandle to a node describing secure memory
- clocks: include clock specifiers corresponding to entries in the
          clock-names property.
- clock-names: optional include
               hdmi-tmds-pll: special pll required by some hdmi-vop design,
                              if there is no hdmi plug, also can reuse for
                              common display pll.
               default-vop-pll: common display pll.

example:

display-subsystem {
	compatible = "rockchip,display-subsystem";
	ports = <&vopl_out>, <&vopb_out>;
	backlight = <&backlight>
	clocks = <&cru PLL_VPLL>, <&cru PLL_CPLL>;
	clock-names = "hdmi-tmds-pll", "default-vop-pll";
};