Fit images and EFI_LOAD_FILE2_PROTOCOL

[Heinrich Schuchardt]

Hello Ilias, hello Christian,

with commit ec80b4735a59 ("efi_loader: Implement FileLoad2 for initramfs
loading") Ilias provided the possibility to specify a device path
(CONFIG_EFI_INITRD_FILESPEC) from which an initial RAM disk can be
served via the EFI_FILE_LOAD2_PROTOCOL.

Ard extended the Linux EFI stub to allow loading the initial RAM disk
via the EFI_FILE_LOAD2_PROTOCOL with the utmost priority.

With commit ecc7fdaa9ef1 ("bootm: Add a bootm command for type
IH_OS_EFI") Cristian enabled signed FIT images that contain a device
tree and a UEFI binary (enabled by CONFIG_BOOTM_EFI=y).

In the DTE calls we have discussed that it is unfortunate that we do not
have a method to validate initial RAM images in the UEFI context.

To me it would look like a good path forward to combine the two ideas:

* Let the signed FIT image (of type IH_OS_EFI) contain a RAM disk
* Pass location and size to the UEFI subsystem and serve them via
  the EFI_FILE_LOAD2_PROTOCOL.

We could also extend the bootefi command to be callable as

   bootefi $kernel_addr_r $ramdisk_addr_r:$filesize $fdt_addr_r

like the booti command to serve an initial RAM disk.

What are your thoughts?

Best regards

Heinrich