linux-kernel - Re: [PATCH 1/2] dt-bindings: hwinfo: Introduce board-id

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Message-Id: <170575419855.2509064.6657399665407807261.robh@kernel.org>
Date: Sat, 20 Jan 2024 06:36:40 -0600
From: Rob Herring <robh@...nel.org>
To: Amrit Anand <quic_amrianan@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, conor+dt@...nel.org, robh+dt@...nel.org, 
 andersson@...nel.org, linux-kernel@...r.kernel.org, agross@...nel.org, 
 krzysztof.kozlowski+dt@...aro.org, devicetree@...r.kernel.org, 
 kernel@...cinc.com, konrad.dybcio@...aro.org, 
 Elliot Berman <quic_eberman@...cinc.com>
Subject: Re: [PATCH 1/2] dt-bindings: hwinfo: Introduce board-id


On Sat, 20 Jan 2024 16:50:48 +0530, Amrit Anand wrote:
> From: Elliot Berman <quic_eberman@...cinc.com>
> 
> Device manufacturers frequently ship multiple boards or SKUs under a
> single software package. These software packages will ship multiple
> devicetree blobs and require some mechanism to pick the correct DTB for
> the board the software package was deployed. Introduce a common
> definition for adding board identifiers to device trees. board-id
> provides a mechanism for bootloaders to select the appropriate DTB which
> is vendor/OEM-agnostic.
> 
> Isn't that what the compatible property is for?
> -----------------------------------------------
> The compatible property can be used for board matching, but requires
> bootloaders and/or firmware to maintain a database of possible strings
> to match against or have complex compatible string matching. Compatible
> string matching becomes complicated when there are multiple versions of
> board: the device tree selector should recognize a DTB that cares to
> distinguish between v1/v2 and a DTB that doesn't make the distinction.
> An eeprom either needs to store the compatible strings that could match
> against the board or the bootloader needs to have vendor-specific
> decoding logic for the compatible string. Neither increasing eeprom
> storage nor adding vendor-specific decoding logic is desirable.
> 
> The solution proposed here is simpler to implement and doesn't require
> updating firmware or bootloader for every new board.
> 
> How is this better than Qualcomm's qcom,msm-id/qcom,board-id?
> -------------------------------------------------------------
> The selection process for devicetrees was Qualcomm-specific and not
> useful for other devices and bootloaders that were not developed by
> Qualcomm because a complex algorithm was used to implement. Board-ids
> provide a matching solution that can be implemented by bootloaders
> without introducing vendor-specific code. Qualcomm uses three
> devicetree properties: msm-id (interchangeably: soc-id), board-id, and
> pmic-id.  This does not scale well for use casese which use identifiers,
> for example, to distinguish between a display panel. For a display
> panel, an approach could be to add a new property: display-id,
> but now	bootloaders need to be updated to also read this property. We
> want to	avoid requiring to update bootloaders with new hardware
> identifiers: a bootloader need only recognize the identifiers it can
> handle.
> 
> Signed-off-by: Elliot Berman <quic_eberman@...cinc.com>
> Signed-off-by: Amrit Anand <quic_amrianan@...cinc.com>
> ---
>  .../devicetree/bindings/hwinfo/board-id.yaml       | 53 ++++++++++++++++++++++
>  1 file changed, 53 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/hwinfo/board-id.yaml
> 

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:
/Documentation/devicetree/bindings/hwinfo/board-id.yaml:23:11: [error] string value is redundantly quoted with any quotes (quoted-strings)
/Documentation/devicetree/bindings/hwinfo/board-id.yaml:25:11: [error] string value is redundantly quoted with any quotes (quoted-strings)

dtschema/dtc warnings/errors:

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/1705749649-4708-2-git-send-email-quic_amrianan@quicinc.com

The base for the series is generally the latest rc1. A different dependency
should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note
that DT_SCHEMA_FILES can be set to your schema file to speed up checking
your schema. However, it must be unset to test all examples with your schema.