linux-kernel - Re: [PATCH v2 3/4] ARM64: dts: meson-gx: add dmcbus and canvas nodes.

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Date:   Wed, 08 Aug 2018 10:41:44 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Maxime Jourdan <maxi.jourdan@...adoo.fr>,
        Kevin Hilman <khilman@...libre.com>
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 3/4] ARM64: dts: meson-gx: add dmcbus and canvas
 nodes.

On Wed, 2018-08-08 at 00:00 +0200, Maxime Jourdan wrote:
> Wrap the canvas node in a syscon node.
> 
> Signed-off-by: Maxime Jourdan <maxi.jourdan@...adoo.fr>
> ---
>  arch/arm64/boot/dts/amlogic/meson-gx.dtsi | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/amlogic/meson-gx.dtsi b/arch/arm64/boot/dts/amlogic/meson-gx.dtsi
> index b8dc4dbb391b..c98198662ae2 100644
> --- a/arch/arm64/boot/dts/amlogic/meson-gx.dtsi
> +++ b/arch/arm64/boot/dts/amlogic/meson-gx.dtsi
> @@ -423,6 +423,23 @@
>  			};
>  		};
>  
> +		dmcbus: bus@...38000 {
> +			compatible = "simple-bus";
> +			reg = <0x0 0xc8838000 0x0 0x1000>;
> +			#address-cells = <2>;
> +			#size-cells = <2>;
> +			ranges = <0x0 0x0 0x0 0xc8838000 0x0 0x1000>;
> +
> +			sysctrl_DMC: system-controller@0 {
> +				compatible = "amlogic,gx-dmc-sysctrl", "syscon", "simple-mfd";
> +				reg = <0x0 0x0 0x0 0x1000>;
> +
> +				canvas: canvas-provider@0 {
> +					compatible = "amlogic,canvas";

If there is only one canvas provider under "sysctrl_DMC" and it has no reg
property , you should not put a unit-address (@0) here. (same for the
documentation patch)

You may have seen unit-address without a reg property used elsewhere (ASoC
simple-card, my recent axg-sound-card), when there is multiple node with the
same node-name (ex: dai-link).

As Martin pointed out, the DT spec says we should not use unit-address unless
there is a reg property. We did not get Rob's view on this and we might have to
update this later on. In your case, unless I missed something, you should
definitely not have it

nitpick regarding the node-name (canvas-provider). If appropriate, we should try
to stick to one of the generic names proposed in the spec. I wonder if the
canvas provider could be viewed as a "memory" or "memory-controller"

So, what about this ? Just a proposition, feel free to comment ;)

	sysctrl_DMC: system-controller@0 {							compatib
le = "amlogic,gx-dmc-sysctrl", "syscon", "simple-mfd";> 		reg =
<0x0 0x0 0x0 0x1000>;

		canvas: memory-controller {
			compatible = "amlogic,canvas";
		}

[...]

> +				};
> +			};
> +		};
> +
>  		hiubus: bus@...3c000 {
>  			compatible = "simple-bus";
>  			reg = <0x0 0xc883c000 0x0 0x2000>;