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

[Dmitry Baryshkov]

On 22/06/2022 12:49, Krzysztof Kozlowski wrote:
> 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@xxxxxxxxxx/
> > > Co-developed-by: Kumar Gala <galak@xxxxxxxxxxxxxx>
> > > Signed-off-by: Kumar Gala <galak@xxxxxxxxxxxxxx>
> > > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> > > ---
> > >    .../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@xxxxxxxxxx>
>
> 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).

This sounds perfect to me. Thanks a lot for your work on sorting this out!

--
With best wishes
Dmitry