linux-kernel - Re: [PATCH 06/12] riscv: dts: allwinner: Add the D1 SoC base devicetree

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Date:   Tue, 16 Aug 2022 11:25:53 +0200
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     Samuel Holland <samuel@...lland.org>, Chen-Yu Tsai <wens@...e.org>,
        linux-sunxi@...ts.linux.dev, Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Heiko Stübner <heiko@...ech.de>
Cc:     Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Subject: Re: [PATCH 06/12] riscv: dts: allwinner: Add the D1 SoC base devicetree

Dne torek, 16. avgust 2022 ob 11:12:05 CEST je Heiko Stübner napisal(a):
> Am Dienstag, 16. August 2022, 09:49:58 CEST schrieb Jernej Škrabec:
> > Dne torek, 16. avgust 2022 ob 09:41:45 CEST je Krzysztof Kozlowski 
napisal(a):
> > > On 15/08/2022 08:08, Samuel Holland wrote:
> > > > +
> > > > +	de: display-engine {
> > > > +		compatible = "allwinner,sun20i-d1-display-engine";
> > > > +		allwinner,pipelines = <&mixer0>, <&mixer1>;
> > > > +		status = "disabled";
> > > > +	};
> > > > +
> > > > +	osc24M: osc24M-clk {
> > > 
> > > lowercase
> > > 
> > > > +		compatible = "fixed-clock";
> > > > +		clock-frequency = <24000000>;
> > > 
> > > This is a property of the board, not SoC.
> > 
> > SoC needs 24 MHz oscillator for correct operation, so each and every board
> > has it. Having it here simplifies board DT files.
> 
> I guess the oscillator is a separate component on each board, right?

Correct.

> And DT obvious is meant to describe the hardware - independently from
> implementation-specific choices.

There is no choice in this case. 24 MHz crystal has to be present.

FWIW, including crystal node in SoC specific DTSI is already common pattern in 
Allwinner ARM SoC DTSI files.

> 
> Starting to discuss which exceptions to allow then might lead to even more
> exceptions.
> 
> Also having to look for a board-component in the soc dtsi also is surprising
> if one gets to the party later on :-) .

As I said, if one is accustomed to Allwinner ARM DT development, it would be 
more surprising to include 24 MHz crystal node in each and every board DT.

Best regards,
Jernej