linux-kernel - Re: [PATCH v2 5/5] arm64: dts: qcom: sc7280: Add herobrine-r1

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Date:   Thu, 3 Feb 2022 21:55:34 +0000
From:   Stephen Boyd <swboyd@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Doug Anderson <dianders@...omium.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        kgodara@...eaurora.org, Matthias Kaehlcke <mka@...omium.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        Prasad Malisetty <pmaliset@...eaurora.org>,
        quic_rjendra@...cinc.com, Andy Gross <agross@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/5] arm64: dts: qcom: sc7280: Add herobrine-r1

Quoting Bjorn Andersson (2022-01-31 08:41:47)
> On Thu 27 Jan 15:16 CST 2022, Stephen Boyd wrote:
>
> > Quoting Bjorn Andersson (2022-01-25 19:01:31)
> > > On Tue 25 Jan 15:46 PST 2022, Doug Anderson wrote:
> > >
> > > > Hi,
> > > >
> > > > On Tue, Jan 25, 2022 at 2:58 PM Stephen Boyd <swboyd@...omium.org> wrote:
> > > > >
> > > > > Quoting Douglas Anderson (2022-01-25 14:44:22)
> > > > > > diff --git a/arch/arm64/boot/dts/qcom/sc7280-herobrine-herobrine-r1.dts b/arch/arm64/boot/dts/qcom/sc7280-herobrine-herobrine-r1.dts
> > > > > > new file mode 100644
> > > > > > index 000000000000..f95273052da0
> > > > > > --- /dev/null
> > > > > > +++ b/arch/arm64/boot/dts/qcom/sc7280-herobrine-herobrine-r1.dts
> > > > > > @@ -0,0 +1,313 @@
> > > > > > +// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
> > > > > > +/*
> > > > > > + * Google Herobrine board device tree source
> > > > > > + *
> > > > > > + * Copyright 2022 Google LLC.
> > > > > > + */
> > > > > > +
> > > > > > +/dts-v1/;
> > > > > > +
> > > > > > +#include "sc7280-herobrine.dtsi"
> > > > > > +
> > > > > > +/ {
> > > > > > +       model = "Google Herobrine (rev1+)";
> > > > > > +       compatible = "google,herobrine", "qcom,sc7280";
> > > > >
> > > > > Can we stop adding "qcom,sc7280" to the board compatible string? It
> > > > > looks out of place. It's the compatible for the SoC and should really be
> > > > > the compatible for the /soc node.
> > > >
> > > > I don't have any objections, but I feel like this is the type of thing
> > > > I'd like Bjorn to have the final say on. What say you, Bjorn?
> > > >
> > >
> > > One practical case I can think of right away, where this matters is in
> > > cpufreq-dt-plat.c where we blocklist qcom,sc7280.
> > >
> > > I don't know if we rely on this in any other places, but I'm not keen on
> > > seeing a bunch of board-specific compatibles sprinkled throughout the
> > > implementation - it's annoying enough having to add each platform to
> > > these drivers.
> >
> > Looking at sc7180, grep only shows cpufreq-dt-plat.c
> >
>
> Good, then we handle all other platform specifics in drivers using
> platform-specific compatibles.
>
> >  $ git grep qcom,sc7180\" -- drivers
> >  drivers/cpufreq/cpufreq-dt-platdev.c:   { .compatible = "qcom,sc7180", },
> >
> > Simplest solution would be to look at / and /soc for a compatible
> > string.
> >
>
> You mean that / would contain the device's compatible and /soc the soc's
> compatible? I'm afraid I don't see how this would help you - you still
> need the compatible in the dts, just now in two places.

I'd like / to contain the board compatible string and /soc to contain
the SoC's compatible string. The two strings are different. In this case
the board compatible at the root would be "google,trogdor-lazor" and the
soc node compatible would be "qcom,sc7180".

>
>
> Either we leave it as is - which follows my interpretation of what the DT
> spec says - or we (and the DT maitainers) agree that it shouldn't be
> there (because this dtb won't run on any random qcom,sc7180 anyways) at
> all.

Sure. Hopefully DT maintainers can chime in here.

As you say, this dtb won't run on any random board that has a
qcom,sc7180 SoC placed on the PCB so having it in the root node
compatible is redundant at the least.