Bug#824954: flash-kernel: please provide a way to integrate with GRUB

[Heinrich Schuchardt <xypron.glpk@gmx.de>]

Let's assume U-Boot uses distroboot as described in doc/README.distro.

Environment variable boot_scripts decides which boot scripts are loaded.

The default value is

boot_scripts=boot.scr.uimg boot.scr

So if you create a boot script named boot.scr.uimg, it will override the 
boot.scr created by flash-kernel.

flash-kernel creates a link /boot/dtb to the actual dtb.

So we do not need any variable part for calling grub.

Create a text file boot.txt like

# Booting Odroid C2 with grub
load mmc 0:2 0x1000000 dtb
load mmc 0:1 0x13000000 efi/debian/grubaa64.efi
bootefi 0x13000000 0x1000000

or

# Booting Odroid XU3/4 with grub
load mmc 0:2 0x43000000 dtb
load mmc 0:1 0x42000000 efi/debian/grubarm.efi
bootefi 0x42000000 0x43000000

Here I assumed that /boot/efi is partition 1 and /boot is partition 2.

Please, carefully verify the script for XU3/4. I have only tested on 
Odroid C2.

Execute
mkimage -T script -d boot.txt uboot.scr.uimg

Copy file uboot.scr.uimg to the boot partition.

Now U-Boot will boot using uboot.scr.uimg and ignore the boot.scr that 
flash-kernel keeps updating.

Best regards

Heinrich Schuchardt