bootstd: Add a bootmeth for Android

Android boot flow is a bit different than a regular Linux distro.
Android relies on multiple partitions in order to boot.

A typical boot flow would be:
1. Parse the Bootloader Control Block (BCB, misc partition)
2. If BCB requested bootonce-bootloader, start fastboot and wait.
3. If BCB requested recovery or normal android, run the following:
3.a. Get slot (A/B) from BCB
3.b. Run AVB (Android Verified Boot) on boot partitions
3.c. Load boot and vendor_boot partitions
3.d. Load device-tree, ramdisk and boot

The AOSP documentation has more details at [1], [2], [3]

This has been implemented via complex boot scripts such as [4].
However, these boot script are neither very maintainable nor generic.
Moreover, DISTRO_DEFAULTS is being deprecated [5].

Add a generic Android bootflow implementation for bootstd.
For this initial version, only boot image v4 is supported.

[1] https://source.android.com/docs/core/architecture/bootloader
[2] https://source.android.com/docs/core/architecture/partitions
[3] https://source.android.com/docs/core/architecture/partitions/generic-boot
[4] https://source.denx.de/u-boot/u-boot/-/blob/master/include/configs/meson64_android.h
[5] https://lore.kernel.org/r/all/[email protected]/

Reviewed-by: Simon Glass <[email protected]>
Reviewed-by: Julien Masson <[email protected]>
Tested-by: Guillaume La Roque <[email protected]>
Signed-off-by: Mattijs Korpershoek <[email protected]>

MAINTAINERS

@@ -939,6 +939,13 @@ F:	include/bootstd.h
 F:	net/eth_bootdevice.c
 F:	test/boot/
 
+BOOTMETH_ANDROID
+M:	Mattijs Korpershoek <[email protected]>
+S:	Maintained
+T:	git https://source.denx.de/u-boot/custodians/u-boot-dfu.git
+F:	boot/bootmeth_android.c
+F:	boot/bootmeth_android.h
+
 BTRFS
 M:	Marek Behún <[email protected]>
 R:	Qu Wenruo <[email protected]>

boot/Kconfig

@@ -494,6 +494,23 @@ config BOOTMETH_GLOBAL
 	  EFI bootmgr, since they take full control over which bootdevs are
 	  selected to boot.
 
+config BOOTMETH_ANDROID
+	bool "Bootdev support for Android"
+	depends on X86 || ARM || SANDBOX
+	depends on CMDLINE
+	select ANDROID_AB
+	select ANDROID_BOOT_IMAGE
+	select CMD_BCB
+	select CMD_FASTBOOT
+	select PARTITION_TYPE_GUID
+	select PARTITION_UUIDS
+	help
+	  Enables support for booting Android using bootstd. Android requires
+	  multiple partitions (misc, boot, vbmeta, ...) in storage for booting.
+
+	  Note that only MMC bootdevs are supported at present. This is caused
+	  by AVB being limited to MMC devices only.
+
 config BOOTMETH_CROS
 	bool "Bootdev support for Chromium OS"
 	depends on X86 || ARM || SANDBOX

boot/Makefile

@@ -66,3 +66,5 @@ obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_VBE_REQUEST) += vbe_request.o
 obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_VBE_SIMPLE) += vbe_simple.o
 obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_VBE_SIMPLE_FW) += vbe_simple_fw.o
 obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_VBE_SIMPLE_OS) += vbe_simple_os.o
+
+obj-$(CONFIG_$(SPL_TPL_)BOOTMETH_ANDROID) += bootmeth_android.o