The software packages are shipped with multiple device tree blobs supporting multiple boards. For instance, suppose we have 3 SoC, each with 4 boards supported, along with 2 PMIC support for each case which would lead to total of 24 DTB files. Along with these configurations, OEMs may also add certain additional board variants. Hence, a mechanism is required to pick the correct DTB for the board on which the software package is deployed. Introduce a unique property for adding board identifiers to device trees. Here, board-id property provides a mechanism for Qualcomm based bootloaders to select the appropriate DTB. 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 parsing and matching. Compatible string matching becomes complicated when there are multiple versions of the same board. It becomes difficult for the device tree selection mechanism to recognize the right DTB to pick, with minor differences in compatible strings. The solution proposed here is simpler to implement and doesn't require the need to update bootloader for every new board. How is this better than Qualcomm's qcom,msm-id/qcom,board-id? ------------------------------------------------------------- Qualcomm's qcom,msm-id/qcom,board-id are not scalable for other distinguishing features as we need to add a new property every time. Board-id property provide a solution that the bootloader can use to select appropriate device tree. Board-id encapsulates soc, board, pmic and oem identifiers. Qualcomm based bootloader can use these key-value pairs to uniquely identify the device tree. This solution scales well for cases where additional identifiers would be needed for device tree selection criteria. Adding a new tuple in "board-id" along with "board-id-type" will help support it. Changes in V2: - Based on comment on V1 related to challenges on designing common bootloader for all the vendors, where different vendors can have different representation of board-id and the best and exact match logic can also be different for different vendors, moving the board-id definition in qcom specific binding. - Adding support for board IDs for all the boards that are in kernel.org. - Adding Qualcomm bootloader best/exact match logic for multi DT selection. - Keeping list of other vendors in CC for comment/awareness related to this requirement - Link to V1: https://lore.kernel.org/all/1705749649-4708-1-git-send-email-quic_amrianan@xxxxxxxxxxx/ Amrit Anand (2): dt-bindings: arm: qcom: Update Devicetree identifiers dt-bindings: qcom: Update DT bindings for multiple DT Documentation/devicetree/bindings/arm/qcom.yaml | 90 +++++++++++++++++++++++++ include/dt-bindings/arm/qcom,ids.h | 86 ++++++++++++++++++++--- 2 files changed, 167 insertions(+), 9 deletions(-) -- 2.7.4
