On Sat, Jan 10, 2026 at 02:00:03PM +0530, 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)
As discussed in the thread here [1], combined DTB is a legacy format which is superceeded by the FIT based [2]. So rather work on FIT based DTB packaging. Along with that extend mkimage tooling support in order to build that FIT based multi DTB image. [1] https://github.com/qualcomm-linux/meta-qcom/pull/1373#discussion_r2684555441 [2] https://github.com/qualcomm-linux/qcom-dtb-metadata/blob/main/Documentation.md -Sumit > > 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` > 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 > >
