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. Amrit Anand (1): dt-bindings: hwinfo: Add Qualcomm's board-id types Elliot Berman (1): dt-bindings: hwinfo: Introduce board-id .../devicetree/bindings/hwinfo/board-id.yaml | 53 +++++++++++++ .../devicetree/bindings/hwinfo/qcom,board-id.yaml | 86 ++++++++++++++++++++++ include/dt-bindings/arm/qcom,ids.h | 68 +++++++++++++++-- 3 files changed, 199 insertions(+), 8 deletions(-) create mode 100644 Documentation/devicetree/bindings/hwinfo/board-id.yaml create mode 100644 Documentation/devicetree/bindings/hwinfo/qcom,board-id.yaml -- 2.7.4
