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

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Message-ID: <19cea8f7c279ef6efb12d1ec0822767d@risingedge.co.za>
Date:   Fri, 14 Jun 2019 20:32:35 +0200
From:   Justin Swartz <justin.swartz@...ingedge.co.za>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Heiko Stuebner <heiko@...ech.de>,
        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

Hi Stephen,

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? :)

Regards
Justin