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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/README.bootcount | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/doc/README.bootcount b/doc/README.bootcount new file mode 100644 index 0000000000..b1c22905c6 --- /dev/null +++ b/doc/README.bootcount @@ -0,0 +1,51 @@ +.. SPDX-License-Identifier: GPL-2.0+ + +Boot Count Limit +================ + +This allows to detect multiple failed attempts to boot Linux. + +After a power-on reset, "bootcount" variable will be initialized with 1, and +each reboot will increment the value by 1. + +If, after a reboot, the new value of "bootcount" exceeds the value of +"bootlimit", then instead of the standard boot action (executing the contents of +"bootcmd") an alternate boot action will be performed, and the contents of +"altbootcmd" will be executed. + +If the variable "bootlimit" is not defined in the environment, the Boot Count +Limit feature is disabled. If it is enabled, but "altbootcmd" is not defined, +then U-Boot will drop into interactive mode and remain there. + +It is the responsibility of some application code (typically a Linux +application) to reset the variable "bootcount", thus allowing for more boot +cycles. + +BOOTCOUNT_EXT +------------- + +This adds support for maintaining boot count in a file on an EXT filesystem. +The file to use is define by: + +SYS_BOOTCOUNT_EXT_INTERFACE +SYS_BOOTCOUNT_EXT_DEVPART +SYS_BOOTCOUNT_EXT_NAME + +The format of the file is: + +==== ================= +type entry +==== ================= +u8 magic +u8 version +u8 bootcount +u8 upgrade_available +==== ================= + +To prevent unattended usage of "altbootcmd" the "upgrade_available" variable is +used. +If "upgrade_available" is 0, "bootcount" is not saved, if "upgrade_available" is +1 "bootcount" is save. +So the Userspace Application must set the "upgrade_available" and "bootcount" +variables to 0, if a boot was successfully. +This also prevents writes on all reboots. |