linux-kernel - Re: [PATCH 1/4] dt-bindings: arm: qcom: document qcom,msm-id and qcom,board-id

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Date:   Sun, 5 Jun 2022 10:07:47 -0500
From:   Rob Herring <robh@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Stephen Boyd <sboyd@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Amit Pundir <amit.pundir@...aro.org>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Rob Clark <robdclark@...il.com>,
        Stephan Gerhold <stephan@...hold.net>,
        Kumar Gala <galak@...eaurora.org>
Subject: Re: [PATCH 1/4] dt-bindings: arm: qcom: document qcom,msm-id and
 qcom,board-id

On Sun, May 29, 2022 at 10:26:26PM +0200, Krzysztof Kozlowski wrote:
> The top level qcom,msm-id and qcom,board-id properties are utilized by
> bootloaders on Qualcomm MSM platforms to determine which device tree
> should be used and passed to the kernel.
> 
> The commit b32e592d3c28 ("devicetree: bindings: Document qcom board
> compatible format") from 2015 was a consensus during discussion about
> upstreaming qcom,msm-id and qcom,board-id fields.  There are however still
> problems with that consensus:
> 1. It was reached 7 years ago but it turned out its implementation did
>    not reach all possible products.
> 
> 2. Initially additional tool (dtbTool) was needed for parsing these
>    fields to create a QCDT image consisting of multiple DTBs, later the
>    bootloaders were improved and they use these qcom,msm-id and
>    qcom,board-id properties directly.
> 
> 3. Extracting relevant information from the board compatible requires
>    this additional tool (dtbTool), which makes the build process more
>    complicated and not easily reproducible (DTBs are modified after the
>    kernel build).
> 
> 4. Some versions of Qualcomm bootloaders expect these properties even
>    when booting with a single DTB.  The community is stuck with these
>    bootloaders thus they require properties in the DTBs.
> 
> Since several upstreamed Qualcomm SoC-based boards require these
> properties to properly boot and the properties are reportedly used by
> bootloaders, document them.

My primary issue here is accepting this will be an endorsement for 
other vendors doing something similar. I'm not against an ID 
property(ies) in the root node, but would rather see something common 
if we do anything.

Rob