[PATCH v1 1/3] efi_loader: Add platform hook for FDT loading

[Simon Glass]

Hi Aswin,

On Tue, 6 Jan 2026 at 05:22, Aswin Murugan
<aswin.murugan at oss.qualcomm.com> wrote:
>
> Introduce a weak function efi_load_platform_fdt() to allow platforms
> to provide custom device tree selection logic. This enables platforms
> with special requirements (such as multi-DTB selection based on
> hardware detection) to load fdt.
>
> The default weak implementation does nothing, Platforms can provide
> a strong implementation to load platform-specific device trees.
>
> Signed-off-by: Aswin Murugan <aswin.murugan at oss.qualcomm.com>
> ---
>  include/efi_loader.h         |  2 ++
>  lib/efi_loader/efi_bootmgr.c |  4 ++++
>  lib/efi_loader/efi_fdt.c     | 23 +++++++++++++++++++++++
>  3 files changed, 29 insertions(+)
>
> diff --git a/include/efi_loader.h b/include/efi_loader.h
> index 3e70ac07055..62c3df48f71 100644
> --- a/include/efi_loader.h
> +++ b/include/efi_loader.h
> @@ -1303,4 +1303,6 @@ int efi_get_distro_fdt_name(char *fname, int size, int seq);
>
>  void efi_load_distro_fdt(efi_handle_t handle, void **fdt, efi_uintn_t *fdt_size);
>
> +void efi_load_platform_fdt(efi_handle_t handle, void **fdt, efi_uintn_t *fdt_size);
> +
>  #endif /* _EFI_LOADER_H */
> diff --git a/lib/efi_loader/efi_bootmgr.c b/lib/efi_loader/efi_bootmgr.c
> index a687f4d8e85..ed06a65feb7 100644
> --- a/lib/efi_loader/efi_bootmgr.c
> +++ b/lib/efi_loader/efi_bootmgr.c
> @@ -1332,6 +1332,10 @@ efi_status_t efi_bootmgr_run(void *fdt)
>                         efi_load_distro_fdt(handle, &fdt_distro, &fdt_size);
>                         fdt = fdt_distro;
>                 }
> +               if (!fdt) {
> +                       efi_load_platform_fdt(handle, &fdt_distro, &fdt_size);
> +                       fdt = fdt_distro;
> +               }
>         }
>
>         /*
> diff --git a/lib/efi_loader/efi_fdt.c b/lib/efi_loader/efi_fdt.c
> index bfaa9cfc207..bfcfd933adf 100644
> --- a/lib/efi_loader/efi_fdt.c
> +++ b/lib/efi_loader/efi_fdt.c
> @@ -78,6 +78,29 @@ int efi_get_distro_fdt_name(char *fname, int size, int seq)
>         return 0;
>  }
>
> +/**
> + * efi_load_platform_fdt() - Platform-specific FDT loading hook (weak)
> + *
> + * @handle:    handle of loaded image
> + * @fdt:       on return device-tree, must be freed via efi_free_pages()
> + * @fdt_size:  buffer size
> + *
> + * This weak function allows platforms to provide custom DTB selection logic.
> + * The default implementation does nothing, allowing the standard distro boot
> + * path to handle FDT loading. Platforms can override this function to
> + * implement custom multi-DTB selection or other platform-specific logic.
> + *
> + * If this function successfully loads a DTB, it should set *fdt to point to
> + * the loaded DTB and return. If it cannot load a DTB, it should set *fdt to
> + * NULL, and the standard distro boot logic will be used as fallback.
> + */
> +__weak void efi_load_platform_fdt(efi_handle_t handle, void **fdt,
> +                                 efi_uintn_t *fdt_size)
> +{
> +       /* Default: do nothing, let standard distro boot handle it */
> +       *fdt = NULL;
> +}
> +
>  /**
>   * efi_load_distro_fdt() - load distro device-tree
>   *
> --
> 2.34.1
>

This is working at the wrong level and a weak function is not a good
idea IMO. You should have a way to determine the compatible string,
not a particular dtb, so that we can use the normal FIT-based
compatibles-string matching to boot, as is done on Qualcomm-based
Chromebooks, for example.

This is the sort of thing that a sysinfo driver could provide.

Also, for this particular platform, are you using grub as well?

Regards,
Simon