Re: [RFC PATCH v1 0/3] efi_loader: Introduce platform hook for FDT selection

[Sumit Garg <sumit.garg@kernel.org>]

Hi Ashwin,

On Tue, Jan 06, 2026 at 05:51:31PM +0530, 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.

As pointed to by folks in the other thread, U-Boot allows to select a
DTB from all the DTBs bundled by the OS in EFI system partition. You can
see the Debian example here for DTBs packaging [1].

> 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.

I think here you are presenting an incomplete picture to the U-Boot
community. You need to show firstly how the multi-DTB FIT image is
prepared first which is described here [2].

From U-Boot point of view, I think this DTB selection logic is useful
which can be used to configure: $fdtfile, see API: configure_env() in
arch/arm/mach-snapdragon/board.c.

However, does this solution also cover OEMs based boards alongside Qcom
reference boards?

> 
> 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
> 

[1] https://packages.debian.org/sid/u-boot-efi-dtb
[2] https://github.com/qualcomm-linux/qcom-dtb-metadata/blob/main/Documentation.md

-Sumit

> 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
> 
> -- 
> 2.34.1
>