linux-kernel - Re: [PATCH 3/4] ARM: dts: rockchip: add display nodes for rk322x

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Date:   Fri, 14 Jun 2019 21:33:12 +0200
From:   Heiko Stuebner <heiko@...ech.de>
To:     Justin Swartz <justin.swartz@...ingedge.co.za>
Cc:     Stephen Boyd <sboyd@...nel.org>,
        linux-rockchip@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, mturquette@...libre.com
Subject: Re: [PATCH 3/4] ARM: dts: rockchip: add display nodes for rk322x

Am Freitag, 14. Juni 2019, 20:32:35 CEST schrieb Justin Swartz:
> On 2019-06-14 19:45, Stephen Boyd wrote:
> >> diff --git a/arch/arm/boot/dts/rk322x.dtsi 
> >> b/arch/arm/boot/dts/rk322x.dtsi
> >> index da102fff96a2..148f9b5157ea 100644
> >> --- a/arch/arm/boot/dts/rk322x.dtsi
> >> +++ b/arch/arm/boot/dts/rk322x.dtsi
> >> @@ -143,6 +143,11 @@
> >> #clock-cells = <0>;
> >> };
> >> 
> >> +       display_subsystem: display-subsystem {
> >> +               compatible = "rockchip,display-subsystem";
> >> +               ports = <&vop_out>;
> >> +       };
> >> +
> > 
> > What is this? It doesn't have a reg property so it looks like a virtual
> > device. Why is it in DT?
> 
> This is a virtual device.
> 
> I assumed it would be acceptable to it find in a device tree due to 
> binding documentation, 
> "Documentation/devicetree/bindings/display/rockchip/rockchip-drm.txt, 
> which states:
> 
> <quote>
> 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.
> </quote>
> 
> Without the "display_subsystem" device node, the HDMI PHY and 
> rockchipdrmfb frame buffer device are not initialized.
> 
> Perhaps I should have included this in my commit message? :)

As Justin said, that is very much common as the root of the components
that make up the drm device and pretty much common in a lot of devicetrees
for the last 5 years and longer ;-) .

Also gpio-keys also don't have a reg property ;-) .

Heiko