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bootstd: Add a bootmeth for Android

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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/20230914165615.1058529-17-sjg@chromium.org/

Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Julien Masson <jmasson@baylibre.com>
Tested-by: Guillaume La Roque <glaroque@baylibre.com>
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
This commit is contained in:
Mattijs Korpershoek
2024-07-10 10:40:05 +02:00
committed by Tom Rini
parent a525656c5b
commit 125d9f3306
6 changed files with 614 additions and 0 deletions
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doc/develop/bootstd.rst
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@@ -95,6 +95,7 @@ bootflows.
Note: it is possible to have a bootmeth that uses a partition or a whole device
directly, but it is more common to use a filesystem.
For example, the Android bootmeth uses a whole device.
Note that some bootmeths are 'global', meaning that they select the bootdev
themselves. Examples include VBE and EFI boot manager. In this case, they
@@ -277,6 +278,9 @@ script_offset_f
script_size_f
Size of the script to load, e.g. 0x2000
vendor_boot_comp_addr_r
Address to which to load the vendor_boot Android image, e.g. 0xe0000000
Some variables are set by script bootmeth:
devtype
@@ -418,6 +422,7 @@ Bootmeth drivers are provided for:
- EFI boot using bootefi from disk
- VBE
- EFI boot using boot manager
- Android bootflow (boot image v4)
Command interface
@@ -786,6 +791,7 @@ To do
Some things that need to be done to completely replace the distro-boot scripts:
- implement extensions (devicetree overlays with add-on boards)
- implement legacy (boot image v2) android boot flow
Other ideas: