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

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Date:   Fri, 14 Jun 2019 13:36:09 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Heiko Stuebner <heiko@...ech.de>,
        Justin Swartz <justin.swartz@...ingedge.co.za>
Cc:     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

Quoting Heiko Stuebner (2019-06-14 12:33:12)
> 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 ;-) .
> 

Do you have a SoC node? If so, this virtual device should live in the
root, away from the nodes that have reg properties and are thus in the
SoC node.