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fc1383ae2b
- Grammar fixes - Clarify explanations Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com> Reviewed-by: Heiko Schocher <hs@denx.de>
54 lines
1.8 KiB
Plaintext
54 lines
1.8 KiB
Plaintext
.. SPDX-License-Identifier: GPL-2.0+
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Boot Count Limit
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================
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This is enabled by CONFIG_BOOTCOUNT_LIMIT.
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This allows to detect multiple failed attempts to boot Linux.
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After a power-on reset, the "bootcount" variable will be initialized to 1, and
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each reboot will increment the value by 1.
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If, after a reboot, the new value of "bootcount" exceeds the value of
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"bootlimit", then instead of the standard boot action (executing the contents of
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"bootcmd"), an alternate boot action will be performed, and the contents of
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"altbootcmd" will be executed.
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If the variable "bootlimit" is not defined in the environment, the Boot Count
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Limit feature is disabled. If it is enabled, but "altbootcmd" is not defined,
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then U-Boot will drop into interactive mode and remain there.
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It is the responsibility of some application code (typically a Linux
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application) to reset the variable "bootcount" to 0 when the system booted
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successfully, thus allowing for more boot cycles.
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CONFIG_BOOTCOUNT_EXT
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--------------------
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This adds support for maintaining boot count in a file on an EXT filesystem.
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The file to use is defined by:
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CONFIG_SYS_BOOTCOUNT_EXT_INTERFACE
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CONFIG_SYS_BOOTCOUNT_EXT_DEVPART
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CONFIG_SYS_BOOTCOUNT_EXT_NAME
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The format of the file is:
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==== =================
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type entry
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==== =================
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u8 magic
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u8 version
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u8 bootcount
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u8 upgrade_available
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==== =================
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To prevent unattended usage of "altbootcmd", the "upgrade_available" variable is
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used.
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If "upgrade_available" is 0, "bootcount" is not saved.
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If "upgrade_available" is 1, "bootcount" is saved.
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So a userspace application should take care of setting the "upgrade_available"
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and "bootcount" variables to 0, if the system boots successfully.
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This also avoids writing the "bootcount" information on all reboots.
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