linux-kernel - Re: [PATCH v2 1/2] dt-bindings: arm: qcom: document qcom,msm-id and qcom,board-id

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Date:   Wed, 22 Jun 2022 11:49:40 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     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>,
        Stephen Boyd <sboyd@...nel.org>
Subject: Re: [PATCH v2 1/2] dt-bindings: arm: qcom: document qcom,msm-id and
 qcom,board-id

On 22/06/2022 11:44, Dmitry Baryshkov wrote:
> On 21/06/2022 21:56, 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.
>>
>> Link: https://lore.kernel.org/r/a3c932d1-a102-ce18-deea-18cbbd05ecab@linaro.org/
>> Co-developed-by: Kumar Gala <galak@...eaurora.org>
>> Signed-off-by: Kumar Gala <galak@...eaurora.org>
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> ---
>>   .../devicetree/bindings/arm/qcom.yaml         | 123 ++++++++++++++++++
>>   include/dt-bindings/arm/qcom,ids.h            |  30 +++++
>>   2 files changed, 153 insertions(+)
>>   create mode 100644 include/dt-bindings/arm/qcom,ids.h
>>
>> diff --git a/Documentation/devicetree/bindings/arm/qcom.yaml b/Documentation/devicetree/bindings/arm/qcom.yaml
>> index 6c38c1387afd..05b98cde4653 100644
>> --- a/Documentation/devicetree/bindings/arm/qcom.yaml
>> +++ b/Documentation/devicetree/bindings/arm/qcom.yaml
>> @@ -403,6 +403,129 @@ properties:
>>                 - qcom,sm8450-qrd
>>             - const: qcom,sm8450
>>   
>> +  # Board compatibles go above
>> +
>> +  qcom,msm-id:
>> +    $ref: /schemas/types.yaml#/definitions/uint32-matrix
>> +    minItems: 1
>> +    maxItems: 8
>> +    items:
>> +      items:
>> +        - description: |
>> +            MSM chipset ID - an exact match value consisting of three bitfields::
>> +             - bits 0-15  - The unique MSM chipset ID
>> +             - bits 16-31 - Reserved; should be 0
>> +        - description: |
>> +            Hardware revision ID - a chipset specific 32-bit ID representing
>> +            the version of the chipset.  It is best a match value - the
>> +            bootloader will look for the closest possible match.
>> +    deprecated: true
>> +    description:
>> +      The MSM chipset and hardware revision use by Qualcomm bootloaders.  It
>> +      can optionally be an array of these to indicate multiple hardware that
>> +      use the same device tree.  It is expected that the bootloader will use
>> +      this information at boot-up to decide which device tree to use when given
>> +      multiple device trees, some of which may not be compatible with the
>> +      actual hardware.  It is the bootloader's responsibility to pass the
>> +      correct device tree to the kernel.
>> +      The property is deprecated - it is not expected on newer boards
>> +      (starting with SM8350).
> 
> I have been thinking about this for quite a while. I think this patch is 
> good.
> 
> With this paragraph (and the corresponding paragraph from the next item) 
> rephrased to remove references to 'newer boards':
> 
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

Great, thanks! And thank you for responding in previous discussions.

I'll remove entire "newer boards ..." part, fix the "two bitfields" and
change the name of the define QCOM_ID_MSM8996. I won't add more board
IDs yet, this can be in following up patches (not only my me).

Best regards,
Krzysztof