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309f77c33a
Add documentation for the bootmeth "rauc", which boots an A/B system with RAUC from MMC. Signed-off-by: Martin Schwan <m.schwan@phytec.de>
57 lines
2.1 KiB
ReStructuredText
57 lines
2.1 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+:
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RAUC Bootmeth
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=============
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This bootmeth provides a way to locate and run an A/B system with RAUC as its
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update client. The booted distro must supply a script on an MMC device
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containing the final boot instructions necessary.
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This bootmeth assumes a symmetric A/B partition layout, with a separate boot
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partition containing the kernel image and another partition for the root
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filesystem each. The partition numbers must be specified with
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``CONFIG_BOOTMETH_RAUC_PARTITIONS``. The content must be a list of pairs, with
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the following syntax: ``1,2 3,4``, where 1 and 3 are the slots' boot partition
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and 2 and 4 the slots' root partition.
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Each pair of boot and rootfs partition form a "slot". The default order in which
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available slots are tried is set through ``CONFIG_BOOTMETH_RAUC_BOOT_ORDER``,
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with the left one tried first.
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The default number of boot tries of each slot is set by
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``CONFIG_BOOTMETH_RAUC_DEFAULT_TRIES``.
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In case no valid slot can be found and/or all slots have zero tries left, the
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boot order and slot tries are reset to their default values, if
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``CONFIG_BOOTMETH_RAUC_RESET_ALL_ZERO_TRIES`` is enabled. This prevents a system
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from locking up in the bootloader and tries booting again after a specified
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number of tries.
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The boot script must be located in each boot partition. The bootmeth searches
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for "boot.scr.uimg" first, then "boot.scr" if not found.
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When the bootflow is booted, the bootmeth sets these environment variables:
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devtype
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device type (e.g. "mmc")
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devnum
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device number, corresponding to the device 'sequence' number
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``dev_seq(dev)``
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distro_bootpart
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partition number of the boot partition on the device (numbered from 1)
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distro_rootpart
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partition number of the rootfs partition on the device (numbered from 1)
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raucargs
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kernel command line arguments needed for RAUC to detect the currently booted
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slot
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The script file must be a FIT or a legacy uImage. It is loaded into memory and
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executed.
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The compatible string "u-boot,distro-rauc" is used for the driver. It is present
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if ``CONFIG_BOOTMETH_RAUC`` is enabled.
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