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 --- v4: Generalize the description of the content of $fdtfile. v3: Add documentation v2: Use a unique GUID to enable future U-Boot independent standardization. Do not try to add the variable on ACPI based systems. --- doc/develop/uefi/uefi.rst | 14 ++++++++++++++ include/efi_loader.h | 5 +++++ lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 49 insertions(+)
diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst index fb16ac743a..702c490831 100644 --- a/doc/develop/uefi/uefi.rst +++ b/doc/develop/uefi/uefi.rst @@ -916,6 +916,20 @@ So our final format of the FilePathList[] is::
Loaded image - end node (0xff) - VenMedia - initrd_1 - [end node (0x01) - initrd_n ...] - end node (0xff)
+EFI variable FdtFile +~~~~~~~~~~~~~~~~~~~~ + +Ideally U-Boot would always expose a device-tree that can be used for booting +any operating systems. Unfortunately operating systems like Linux sometimes +break forward and backward compatibility. In this case there is a need to load +an operating system version specific device-tree. + +U-Boot has an environment variable fdtfile identifying the device-tree file to +load. The content of this variable is exposed as EFI variable Fdtfile, vendor +GUID d45dde69-3bd6-40e0-90d5-6b606aa57730. It contains the device-tree path +name as a NUL terminated ASCII string. On many architectures the file name is +preceded by a vendor directory ('vendor-directory/board-name.dtb'). + Links -----
diff --git a/include/efi_loader.h b/include/efi_loader.h index e24410505f..146e7f1bce 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(0xd45dde69, 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)