Re: [PATCH RFC v3 0/9] dt-bindings: hwinfo: Introduce board-id

[Simon Glass]

Hi Elliot,

On Tue, 21 May 2024 at 12:38, Elliot Berman <quic_eberman@xxxxxxxxxxx> wrote:
>
> 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.
>
> This series is based off a talk I gave at EOSS NA 2024 [1]. There is
> some further discussion about how to do devicetree selection in the
> boot-architecture mailing list [2].
>
> [1]: https://sched.co/1aBFy
> [2]: https://lists.linaro.org/archives/list/boot-architecture@xxxxxxxxxxxxxxxx/thread/DZCZSOCRH5BN7YOXEL2OQKSDIY7DCW2M/
>
> Quick summary
> -------------
> This series introduces a new subnode in the root:
> / {
>         board-id {
>                 some-hw-id = <value>;
>                 other-hw-id = <val1>, <val2>;
>         };
> };
>
> Firmware provides a mechanism to fetch the values of "some-hw-id" and
> "other-hw-id" based on the property name. I'd like to leave exact
> mechanism data out of the scope of this proposal to keep this proposal
> flexible because it seems architecture specific, although I think we we
> should discuss possible approaches. A DTB matches if firmware can
> provide a matching value for every one of the properties under
> /board-id. In the above example, val1 and val2 are both valid values and
> firmware only provides the one that actually describes the board.
>
> It's expected that devicetree's board-id don't describe all the
> properties firmware could provide. For instance, a devicetree overlay
> may only care about "other-hw-id" and not "some-hw-id". Thus, it need
> only mention "other-hw-id" in its board-id node.
>
> 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 implement 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.

That is not necessary, though. The compatible string should be enough.

>
> 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.
>
> Notes about the patches
> -----------------------
> In my opinion, most of the patches in this series should be submitted to
> libfdt and/or dtschema project. I've made them apply on the kernel tree
> to be easier for other folks to pick them up and play with them. As the
> patches evolve, I can send them to the appropriate projects.
>
> Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx>
> ---
> Changes in v3:
>  - Follow new "/board-id {}" approach, which uses key-value pairs
>  - Add match algorithm in libfdt and some examples to demo how the
>    selection could work in tools/board-id
>
> Changes in V2:
>  - Addressed few comments related to board-id, and DDR type.
>  - Link to V2:  https://lore.kernel.org/all/a930a3d6-0846-a709-8fe9-44335fec92ca@xxxxxxxxxxx/#r
>
> ---
> Amrit Anand (1):
>       dt-bindings: arm: qcom: Update Devicetree identifiers
>
> Elliot Berman (8):
>       libfdt: board-id: Implement board-id scoring
>       dt-bindings: board: Introduce board-id
>       fdt-select-board: Add test tool for selecting dtbs based on board-id
>       dt-bindings: board: Document board-ids for Qualcomm devices
>       arm64: boot: dts: sm8650: Add board-id
>       arm64: boot: dts: qcom: Use phandles for thermal_zones
>       arm64: boot: dts: qcom: sm8550: Split into overlays
>       tools: board-id: Add test suite
>
>  .../devicetree/bindings/board/board-id.yaml        |  24 ++++
>  .../devicetree/bindings/board/qcom,board-id.yaml   | 144 ++++++++++++++++++++
>  arch/arm64/boot/dts/qcom/Makefile                  |   4 +
>  arch/arm64/boot/dts/qcom/pm8010.dtsi               |  62 ++++-----
>  arch/arm64/boot/dts/qcom/pm8550.dtsi               |  32 ++---
>  arch/arm64/boot/dts/qcom/pm8550b.dtsi              |  36 +++--
>  arch/arm64/boot/dts/qcom/pm8550ve.dtsi             |  38 +++---
>  arch/arm64/boot/dts/qcom/pm8550vs.dtsi             | 128 +++++++++--------
>  arch/arm64/boot/dts/qcom/pmr735d_a.dtsi            |  38 +++---
>  arch/arm64/boot/dts/qcom/pmr735d_b.dtsi            |  38 +++---
>  .../dts/qcom/{sm8550-mtp.dts => sm8550-mtp.dtso}   |  24 +++-
>  .../dts/qcom/{sm8550-qrd.dts => sm8550-qrd.dtso}   |  22 ++-
>  .../boot/dts/qcom/{sm8550.dtsi => sm8550.dts}      |  10 +-
>  arch/arm64/boot/dts/qcom/sm8650-mtp.dts            |   6 +
>  arch/arm64/boot/dts/qcom/sm8650-qrd.dts            |   6 +
>  arch/arm64/boot/dts/qcom/sm8650.dtsi               |   2 +-
>  include/dt-bindings/arm/qcom,ids.h                 |  86 ++++++++++--
>  scripts/dtc/.gitignore                             |   1 +
>  scripts/dtc/Makefile                               |   3 +-
>  scripts/dtc/fdt-select-board.c                     | 126 +++++++++++++++++
>  scripts/dtc/libfdt/fdt_ro.c                        |  76 +++++++++++
>  scripts/dtc/libfdt/libfdt.h                        |  54 ++++++++
>  tools/board-id/test.py                             | 151 +++++++++++++++++++++
>  23 files changed, 901 insertions(+), 210 deletions(-)
> ---
> base-commit: e8f897f4afef0031fe618a8e94127a0934896aba
> change-id: 20240112-board-ids-809ff0281ee5
>
> Best regards,
> --
> Elliot Berman <quic_eberman@xxxxxxxxxxx>
>

I am just picking up the discussion here, which was started on another thread.

I can't see why this new feature is needed. We should be able to use
compatible strings, as we do now. I added a 'usage' section to the FIT
spec [1] which might help. I also incorporated the board revision and
variant information and some notes on how to add to the available
suffixes.

Does that handle your use case?

Regards,
Simon

[1] https://github.com/open-source-firmware/flat-image-tree/blob/main/source/chapter3-usage.rst