[RFC PATCH 3/3] efi: Bump the Linux EFI stub major version number to #1

[Ard Biesheuvel <ardb@kernel.org>]

Now that we have introduced new, generic ways for the OS loader to
interface with Linux kernels during boot, we need to record this
fact in a way that allows loaders to discover this information, and
fall back to the existing methods for older kernels.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 include/linux/pe.h | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/include/linux/pe.h b/include/linux/pe.h
index e0869f3eadd6..8ad71d763a77 100644
--- a/include/linux/pe.h
+++ b/include/linux/pe.h
@@ -10,7 +10,25 @@
 
 #include <linux/types.h>
 
-#define LINUX_EFISTUB_MAJOR_VERSION		0x0
+/*
+ * Linux EFI stub v1.0 adds the following functionality:
+ * - Loading initrd from the LINUX_EFI_INITRD_MEDIA_GUID device path,
+ * - Loading/starting the kernel from firmware that targets a different
+ *   machine type, via the entrypoint exposed in the .compat PE/COFF section.
+ *
+ * The recommended way of loading and starting v1.0 or later kernels is to use
+ * the LoadImage() and StartImage() EFI boot services, and expose the initrd
+ * via the LINUX_EFI_INITRD_MEDIA_GUID device path.
+ *
+ * Versions older than v1.0 support initrd loading via the image load options
+ * (using initrd=, limited to the volume from which the kernel itself was
+ * loaded), or via arch specific means (bootparams, DT, etc).
+ *
+ * On x86, LoadImage() and StartImage() can be omitted if the EFI handover
+ * protocol is implemented, which can be inferred from the version,
+ * handover_offset and xloadflags fields in the bootparams structure.
+ */
+#define LINUX_EFISTUB_MAJOR_VERSION		0x1
 #define LINUX_EFISTUB_MINOR_VERSION		0x0
 
 #define MZ_MAGIC	0x5a4d	/* "MZ" */
-- 
2.17.1