linux-kernel - Re: [PATCH v3 1/8] dt-bindings: arm: qcom: Document MSM8939 SoC binding

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Message-ID: <Y8gTjSkecPvvZtYg@gerhold.net>
Date:   Wed, 18 Jan 2023 16:43:09 +0100
From:   Stephan Gerhold <stephan@...hold.net>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Cc:     agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
        djakov@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, benl@...areup.com,
        shawn.guo@...aro.org, fabien.parent@...aro.org, leo.yan@...aro.org,
        dmitry.baryshkov@...aro.org,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v3 1/8] dt-bindings: arm: qcom: Document MSM8939 SoC
 binding

On Wed, Jan 18, 2023 at 12:05:50PM +0000, Bryan O'Donoghue wrote:
> On 18/01/2023 08:47, Stephan Gerhold wrote:
> > On Tue, Jan 17, 2023 at 02:48:39AM +0000, Bryan O'Donoghue wrote:
> > > Document the MSM8939 and supported boards in upstream Sony "Tulip" M4 Aqua
> > > and Square APQ8039 T2.
> > > 
> > > MSM8939 is one of the older SoCs so we need to expand the list of
> > > qcom,board-ids to allow for the bootloader DTS board-id matching
> > > dependency.
> > > 
> > 
> > The original LK bootloaders cannot boot your msm8939.dtsi correctly,
> > because a spin-table implementation is required to get the other CPU
> > cores up. This means that a modified bootloader is always needed from
> > the upstream point of view, since I doubt anyone wants to use these
> > devices with a single core only. lk2nd (as the primary spin-table
> > implementation right now) has never required qcom,board-ids and any
> > custom LK would be easy to patch to ignore these.
> 
> The system boots just fine with the shipped LK. We get display, USB, SD,
> WiFi.
> 
> We just don't support booting the second cluster via any other means than
> lk2nd right now.
> 
> You could also not use lk2nd, stick with your default LK and import LPM
> patches.
> 

My point is: If you import out of tree LPM patches you can also just
import an extra patch that adds the qcom,board-id property where needed.

The qcom,board-id is only needed/used in configurations where you need
to add those extra LPM patches on top anyway. Those configurations are
(sadly) not supported from the upstream point of view, since only PSCI
or spin-table are supposed to be used for CPU bring-up/idle.

Anyway, for me personally there is no difference if the funky
qcom,board-id properties are there or not, so I'll leave it up to
Rob/Krzysztof to decide if the board-id exception is warranted here or
not. :)

Thanks,
Stephan