On Mon, Jan 12, 2026 at 02:48:21PM +0100, Casey Connolly wrote: > Hi Aswin, > > On 10/01/2026 09:30, Aswin Murugan wrote: > > Thanks everyone for all the valuable feedback. I appreciate the detailed > > reviews and want to address the concerns raised. > > > > I should have been clearer upfront about what makes Qualcomm platforms > > different here. Qualcomm has its own combined-dtb format that's been > > used across Linux products. The format is documented in [1] and the > > combined dtb file is placed in a separate dtb partition > > > > The combined-dtb file contains multiple DTBs concatenated together as a > > single dtb file, each with Qualcomm-specific properties: > > - qcom,msm-id (platform ID and SoC revision) > > - qcom,board-id (board variant and subtype) > > - qcom,pmic-id (PMIC models - up to 4) > > > > At runtime, we read hardware info from SMEM (shared memory interface > > with the firmware) and match it against these properties to pick the > > right DTB. > > > > *Why Existing Approaches Don't Quite Fit* > > > > After reviewing the feedback from Heinrich, Ilias, Simon & Sumith, I > > realize the core issue is that all the existing U-Boot mechanisms assume > > separate DTB files on the ESP: > > > > VisionFive2 approach: Uses EEPROM detection in SPL and sets `$fdtfile` > > to point to individual files like `dtb/starfive/jh7110-milkv-mars.dtb`, > > `dtb/starfive/jh7110-starfive-visionfive-2-v1.3b.dtb` > > > > eficonfig and distro boot: These mechanisms work great for selecting > > between multiple DTB files. > > > > The common thread is they all expect individual DTB files, while > > Qualcomm's deployment model uses a single combined-dtb.dtb file that > > requires parsing and extraction. This is the fundamental gap we're > > trying to bridge. > > > > I agree with Simon that using the weak function approach is not an > > ideal solution. we should be avoiding adding hooks in the EFI loader. > > Instead, we need to handle this at the board level and work with the > > existing `$fdtfile` mechanism. > > > > *Proposed Approach* > > > > Based on all the feedback, here's the revised plan: > > For v2: > > 1. In board code: Parse combined-dtb.dtb, extract the matching DTB, > > write to ESP as `dtb/qcom-<board>.dtb` > > In board code - this should be a new file in mach-snapdragon with a new > config option. > > I don't think it's correct to write to the ESP, that's a very good way > to frustrate users and developers imo. Once the proper FDT has been > found it can be installed as the default for EFI booting by setting > $fdt_addr to point to it (see efi_install_fdt() in > lib/efi_loader/efi_helper.c), as well as setting $fdtfile > > This way fdt_addr can be overwritten during boot by the user, and if > there is an FDT found on the ESP then we can be sure it was put there by > the distro or user and it should be used instead. > > So in the end the priority of where the FDT is sourced from will look > like this: > > 1. OS loader (GRUB/sd-boot) > 2. FDT loaded/configured by user (e.g. in eficonfig) > 3. DTB found on the ESP by U-Boot (based on $fdtfile) > 4. FDT from qcom-specific dtb partition > 5. U-Boot's own FDT > > I think this strikes a good balance without imposing confusing logic on > the user, particularly if there is a nice log message when the FDT is > installed from the qcom combined DTB.
Sounds reasonable to me. -Sumit > > Kind regards, > > > 3. Set `$fdtfile` to point to the extracted file > > 4. Let standard EFI mechanisms handle the rest > > 5. Drop the weak function approach entirely > > > > Does this approach address the concerns raised, or suggest a different > > direction? I'm particularly interested in feedback on runtime DTB > > extraction to ESP is acceptable, or if there's a better way to bridge > > between our combined-dtb format and U-Boot's expectations. > > > > [1] https://docs.qualcomm.com/doc/80-70023-27/topic/ > > configure_and_secure_boot_with_systemd_boot_and_uki.html#multi-dtb-support > > > > Thanks, > > Aswin > > > > On 1/6/2026 5:51 PM, Aswin Murugan wrote: > >> This RFC patch series introduces a weak function hook to allow > >> platforms to > >> provide custom device tree selection logic while keeping common EFI > >> loader code generic. > >> > >> Background: > >> Currently, EFI loader supports loading a single DTB file. > >> Qualcomm platforms require special multi-DTB selection logic that: > >> - Reads hardware information from SMEM (Shared Memory) > >> - Selects the appropriate device tree from a combined DTB file based on: > >> * Platform ID (SoC variant) > >> * Board variant and subtype > >> * PMIC configuration > >> * SoC revision. > >> > >> Solution: > >> Introduce `efi_load_platform_fdt()` as a weak function: > >> - Weak implementation in lib/efi_loader/efi_fdt.c (defaults to no-op) > >> - Called from efi_bootmgr_run() after efi_load_distro_fdt() > >> - Qualcomm override in arch/arm/mach-snapdragon/efi_fdt_qcom.c > >> > >> Aswin Murugan (3): > >> efi_loader: Add platform hook for FDT loading > >> soc: qcom: smem: Added socinfo header file > >> mach-snapdragon: Implement Qualcomm multi-DTB selection > >> > >> arch/arm/mach-snapdragon/Makefile | 1 + > >> arch/arm/mach-snapdragon/efi_fdt_qcom.c | 339 ++++++++++++++++++++++++ > >> include/soc/qcom/socinfo.h | 114 ++++++++ > >> lib/efi_loader/efi_fdt.c | 34 +++ > >> 4 files changed, 488 insertions(+) > >> create mode 100644 arch/arm/mach-snapdragon/efi_fdt_qcom.c > >> create mode 100644 include/soc/qcom/socinfo.h > >> > > -- > // Casey (she/her) >
