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Frédéric Danisdf928f82020-03-17 17:59:09 +01001.. SPDX-License-Identifier: GPL-2.0+
2
3Boot Count Limit
4================
5
6This allows to detect multiple failed attempts to boot Linux.
7
8After a power-on reset, "bootcount" variable will be initialized with 1, and
9each reboot will increment the value by 1.
10
11If, after a reboot, the new value of "bootcount" exceeds the value of
12"bootlimit", then instead of the standard boot action (executing the contents of
13"bootcmd") an alternate boot action will be performed, and the contents of
14"altbootcmd" will be executed.
15
16If the variable "bootlimit" is not defined in the environment, the Boot Count
17Limit feature is disabled. If it is enabled, but "altbootcmd" is not defined,
18then U-Boot will drop into interactive mode and remain there.
19
20It is the responsibility of some application code (typically a Linux
21application) to reset the variable "bootcount", thus allowing for more boot
22cycles.
23
24BOOTCOUNT_EXT
25-------------
26
27This adds support for maintaining boot count in a file on an EXT filesystem.
28The file to use is define by:
29
30SYS_BOOTCOUNT_EXT_INTERFACE
31SYS_BOOTCOUNT_EXT_DEVPART
32SYS_BOOTCOUNT_EXT_NAME
33
34The format of the file is:
35
36==== =================
37type entry
38==== =================
39u8 magic
40u8 version
41u8 bootcount
42u8 upgrade_available
43==== =================
44
45To prevent unattended usage of "altbootcmd" the "upgrade_available" variable is
46used.
47If "upgrade_available" is 0, "bootcount" is not saved, if "upgrade_available" is
481 "bootcount" is save.
49So the Userspace Application must set the "upgrade_available" and "bootcount"
50variables to 0, if a boot was successfully.
51This also prevents writes on all reboots.