mirror of
https://github.com/AsahiLinux/u-boot
synced 2024-11-28 07:31:15 +00:00
586a1bf5b2
Convert Android documentation from regular txt format to Sphinx (RST).
Also add Android index.rst file and reference it in root index.rst, so
that Android documentation is visible.
Test:
$ make htmldocs
$ xdg-open doc/output/index.html
Signed-off-by: Sam Protsenko <joe.skb7@gmail.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
72 lines
2.1 KiB
ReStructuredText
72 lines
2.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
|
|
|
|
Android A/B updates
|
|
===================
|
|
|
|
Overview
|
|
--------
|
|
|
|
A/B system updates ensures modern approach for system update. This feature
|
|
allows one to use two sets (or more) of partitions referred to as slots
|
|
(normally slot A and slot B). The system runs from the current slot while the
|
|
partitions in the unused slot can be updated [1]_.
|
|
|
|
A/B enablement
|
|
--------------
|
|
|
|
The A/B updates support can be activated by specifying next options in
|
|
your board configuration file::
|
|
|
|
CONFIG_ANDROID_AB=y
|
|
CONFIG_CMD_AB_SELECT=y
|
|
|
|
The disk space on target device must be partitioned in a way so that each
|
|
partition which needs to be updated has two or more instances. The name of
|
|
each instance must be formed by adding suffixes: ``_a``, ``_b``, ``_c``, etc.
|
|
For example: ``boot_a``, ``boot_b``, ``system_a``, ``system_b``, ``vendor_a``,
|
|
``vendor_b``.
|
|
|
|
As a result you can use ``ab_select`` command to ensure A/B boot process in your
|
|
boot script. This command analyzes and processes A/B metadata stored on a
|
|
special partition (e.g. ``misc``) and determines which slot should be used for
|
|
booting up.
|
|
|
|
Command usage
|
|
-------------
|
|
|
|
.. code-block:: none
|
|
|
|
ab_select <slot_var_name> <interface> <dev[:part_number|#part_name]>
|
|
|
|
for example::
|
|
|
|
=> ab_select slot_name mmc 1:4
|
|
|
|
or::
|
|
|
|
=> ab_select slot_name mmc 1#misc
|
|
|
|
Result::
|
|
|
|
=> printenv slot_name
|
|
slot_name=a
|
|
|
|
Based on this slot information, the current boot partition should be defined,
|
|
and next kernel command line parameters should be generated:
|
|
|
|
* ``androidboot.slot_suffix=``
|
|
* ``root=``
|
|
|
|
For example::
|
|
|
|
androidboot.slot_suffix=_a root=/dev/mmcblk1p12
|
|
|
|
A/B metadata is organized according to AOSP reference [2]_. On the first system
|
|
start with A/B enabled, when ``misc`` partition doesn't contain required data,
|
|
the default A/B metadata will be created and written to ``misc`` partition.
|
|
|
|
References
|
|
----------
|
|
|
|
.. [1] https://source.android.com/devices/tech/ota/ab
|
|
.. [2] https://android.googlesource.com/platform/bootable/recovery/+/refs/tags/android-10.0.0_r25/bootloader_message/include/bootloader_message/bootloader_message.h
|