efi: Add support for loading U-Boot through an EFI stub

It is useful to be able to load U-Boot onto a board even if is it already
running EFI. This can allow access to the U-Boot command interface, flexible
booting options and easier development.

The easiest way to do this is to build U-Boot as a binary blob and have an
EFI stub copy it into RAM. Add support for this feature, targeting 32-bit
initially.

Also add a way to detect when U-Boot has been loaded via a stub. This goes
in common.h since it needs to be widely available so that we avoid redoing
initialisation that should be skipped.

Signed-off-by: Simon Glass <sjg@chromium.org>
Improvements to how the payload is built:
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/lib/efi/Kconfig b/lib/efi/Kconfig
index b23ba5b5041..919e314a0ce 100644
--- a/lib/efi/Kconfig
+++ b/lib/efi/Kconfig
@@ -20,6 +20,11 @@ config EFI_APP
 	  command prompt and memory and I/O functions. Use 'reset' to return
 	  to EFI.
 
+config EFI_STUB
+	bool "Support running as an EFI payload"
+
+endchoice
+
 config EFI_RAM_SIZE
 	hex "Amount of EFI RAM for U-Boot"
 	depends on EFI_APP
@@ -30,4 +35,20 @@ config EFI_RAM_SIZE
 	  other smaller amounts) and it can never be increased after that.
 	  It is used as the RAM size in with U-Boot.
 
+choice
+	prompt "EFI 32/64-bit selection"
+	depends on EFI_STUB
+	help
+	  EFI does not support mixing 32-bit and 64-bit modes. This is a
+	  significant problem because it means that you must build a stub with
+	  the correct type for EFI to load it correctly. If you are using
+	  32-bit EFI, select 32-bit here, else select 64-bit. Failure to do
+	  this may produce no error message - it just won't start!
+
+config EFI_STUB_32BIT
+	bool "Produce a stub for running with 32-bit EFI"
+
+config EFI_STUB_64BIT
+	bool "Produce a stub for running with 64-bit EFI"
+
 endchoice