Re: [PATCH v2 1/1] efi_loader: expose the device-tree file name

On Tue, 17 Oct 2023 at 16:50, Heinrich Schuchardt heinrich.schuchardt@canonical.com wrote:

Forward and backward compatibility of Linux kernel device-trees is sometimes missing. One solution approach is to load a kernel specific device-tree. This can either be done via a U-Boot scripts (like the one generated by Debian package flash-kernel or by a boot loader like GRUB. The boot loader approach currently requires to know the device-tree name before first boot which makes it unusable for generic images.

Expose the device-tree file name as EFI variable FdtFile. This will allow bootloaders to load a kernel specific device-tree.

The variable will not be exposed on ACPI based systems or if the environment variable fdtfile is not defined.

Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com

v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems.

---

include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 2 files changed, 35 insertions(+)

diff --git a/include/efi_loader.h b/include/efi_loader.h index e24410505f..2faa1c191c 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -152,6 +152,11 @@ static inline efi_status_t efi_launch_capsules(void) EFI_GUID(0x8108ac4e, 0x9f11, 0x4d59, \ 0x85, 0x0e, 0xe2, 0x1a, 0x52, 0x2c, 0x59, 0xb2)

+/* Vendor GUID for the FdtFile variable */ +#define VENDOR_FDTFILE_GUID \

•   EFI_GUID(d45dde69, 0x3bd6, 0x40e0, \
  

•            0x90, 0xd5, 0x6b, 0x60, 0x6a, 0xa5, 0x77, 0x30)
  

/* Use internal device tree when starting UEFI application */ #define EFI_FDT_USE_INTERNAL NULL

diff --git a/lib/efi_loader/efi_setup.c b/lib/efi_loader/efi_setup.c index e6de685e87..71bcde645b 100644 --- a/lib/efi_loader/efi_setup.c +++ b/lib/efi_loader/efi_setup.c @@ -17,6 +17,8 @@

efi_status_t efi_obj_list_initialized = OBJ_LIST_NOT_INITIALIZED;

+efi_guid_t vendor_fdtfile_guid = VENDOR_FDTFILE_GUID;

/*

• Allow unaligned memory access.

@@ -26,6 +28,27 @@ void __weak allow_unaligned(void) { }

+/**

• • efi_init_fdtfile() - set EFI variable FdtFile
• • Return: status code
• */

+static efi_status_t efi_init_fdtfile(void) +{

•   char *val;
  

•   val = env_get("fdtfile");
  

•   if (!val)
  

•           return EFI_SUCCESS;
  

•   return efi_set_variable_int(u"FdtFile",
  

•                               &vendor_fdtfile_guid,
  

•                               EFI_VARIABLE_BOOTSERVICE_ACCESS |
  

•                               EFI_VARIABLE_RUNTIME_ACCESS |
  

•                               EFI_VARIABLE_READ_ONLY,
  

•                               strlen(val) + 1, val, false);
  

+}

/**

• efi_init_platform_lang() - define supported languages

@@ -250,6 +273,13 @@ efi_status_t efi_init_obj_list(void) if (ret != EFI_SUCCESS) goto out;

•   /* Define EFI variable FdtFile */
  

•   if (!CONFIG_IS_ENABLED(GENERATE_ACPI_TABLE)) {
  

•           ret = efi_init_fdtfile();
  

•           if (ret != EFI_SUCCESS)
  

•                   goto out;
  

•   }
  

•   /* Indicate supported features */
    ret = efi_init_os_indications();
    if (ret != EFI_SUCCESS)
  

-- 2.40.1

Reviewed-by: Ilias Apalodimas ilias.apalodimas@linaro.org