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

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Date:   Mon, 31 Jan 2022 08:50:52 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Stephen Boyd <swboyd@...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>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <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

Hi,

On Mon, Jan 31, 2022 at 8:41 AM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> 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.
>
>
> 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.

I'm curious what part of the DT spec says that we should have the SoC
in there? I know I've always done it, but it's always just been
following the examples of what was done before. When talking about the
root node, I see this in the `devicetree-specification-v0.4-rc1` spec:

---

Specifies a list of platform architectures with which this platform is
compatible. This property can be used by operating systems in
selecting platform specific code. The recommended form of the property
value is: "manufacturer,model"

For example:
compatible = "fsl,mpc8572ds"

---

That doesn't say anything about putting the SoC there.


I would also note that I'd be at least moderately inclined to land
things as-is and deal with this in a follow-up patch, though I'm happy
to spin if that's what people agree upon too. This is not a new
problem and so it doesn't seem like it makes sense to glom dealing
with it into this patch series...

-Doug