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]>

1 files changed, 29 insertions, 0 deletions

diff --git a/boot/bootmeth_android.h b/boot/bootmeth_android.h
new file mode 100644
index 00000000000..a57fad9f011
--- /dev/null
+++ b/boot/bootmeth_android.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Bootmethod for Android
+ *
+ * Copyright (C) 2024 BayLibre, SAS
+ * Written by Mattijs Korpershoek <[email protected]>
+ */
+
+enum android_boot_mode {
+	ANDROID_BOOT_MODE_NORMAL = 0,
+
+	/*
+	 * Android "recovery" is a special boot mode that uses another ramdisk.
+	 * It can be used to "factory reset" a board or to flash logical partitions
+	 * It operates in 2 modes: adb or fastbootd
+	 * To enter recovery from Android, we can do:
+	 * $ adb reboot recovery
+	 * $ adb reboot fastboot
+	 */
+	ANDROID_BOOT_MODE_RECOVERY,
+
+	/*
+	 * Android "bootloader" is for accessing/reflashing physical partitions
+	 * Typically, this will launch a fastboot process in U-Boot.
+	 * To enter "bootloader" from Android, we can do:
+	 * $ adb reboot bootloader
+	 */
+	ANDROID_BOOT_MODE_BOOTLOADER,
+};