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93767c5a8f
Add initial documentation for the Android bootmeth. Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com> Reviewed-by: Simon Glass <sjg@chromium.org>
40 lines
1.6 KiB
ReStructuredText
40 lines
1.6 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+:
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Android Bootmeth
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================
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Android provides a mechanism for booting its Operating System from eMMC storage,
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described on `source.android.com <https://source.android.com/docs/core/architecture/bootloader>`_.
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Android has strong requirements about partitioning layout which are described
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`here <https://source.android.com/docs/core/architecture/partitions>`_.
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Because multiple partitions are required, this bootmeth only operates on whole mmc
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devices which have a valid partition table.
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When invoked on a bootdev, this bootmeth searches for the ``misc`` partition in order
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to read the *boot mode*, which can be one of following:
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Normal
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Boot the regular Android Operating System.
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Recovery
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Boot a slimmed down Recovery Operating System. Can be used
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to factory reset the device or to apply system updates.
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Bootloader
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Stay in U-Boot and wait for fastboot commands from the host.
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After the *boot mode* has been determined, this bootmeth will read the *slot suffix*
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from the ``misc`` partition. For details about slots, see
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`the AOSP documentation <https://source.android.com/docs/core/ota/ab#slots>`_.
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When both the *boot mode* and the *slot suffix* are known, the bootflow is created.
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When the bootflow is booted, the bootmeth reads the kernel, the boot arguments and
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the vendor ramdisk.
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It then boots the kernel using bootm. The relevant devicetree blob is extracted
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from the ``boot`` partition based on the ``adtb_idx`` environment variable.
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The compatible string "u-boot,android" is used for the driver. It is present
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if `CONFIG_BOOTMETH_ANDROID` is enabled.
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