| Frédéric Danis | df928f8 | 2020-03-17 17:59:09 +0100 | [diff] [blame] | 1 | .. SPDX-License-Identifier: GPL-2.0+ |
| 2 | |
| 3 | Boot Count Limit |
| 4 | ================ |
| 5 | |
| 6 | This allows to detect multiple failed attempts to boot Linux. |
| 7 | |
| 8 | After a power-on reset, "bootcount" variable will be initialized with 1, and |
| 9 | each reboot will increment the value by 1. |
| 10 | |
| 11 | If, 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 | |
| 16 | If the variable "bootlimit" is not defined in the environment, the Boot Count |
| 17 | Limit feature is disabled. If it is enabled, but "altbootcmd" is not defined, |
| 18 | then U-Boot will drop into interactive mode and remain there. |
| 19 | |
| 20 | It is the responsibility of some application code (typically a Linux |
| 21 | application) to reset the variable "bootcount", thus allowing for more boot |
| 22 | cycles. |
| 23 | |
| 24 | BOOTCOUNT_EXT |
| 25 | ------------- |
| 26 | |
| 27 | This adds support for maintaining boot count in a file on an EXT filesystem. |
| 28 | The file to use is define by: |
| 29 | |
| 30 | SYS_BOOTCOUNT_EXT_INTERFACE |
| 31 | SYS_BOOTCOUNT_EXT_DEVPART |
| 32 | SYS_BOOTCOUNT_EXT_NAME |
| 33 | |
| 34 | The format of the file is: |
| 35 | |
| 36 | ==== ================= |
| 37 | type entry |
| 38 | ==== ================= |
| 39 | u8 magic |
| 40 | u8 version |
| 41 | u8 bootcount |
| 42 | u8 upgrade_available |
| 43 | ==== ================= |
| 44 | |
| 45 | To prevent unattended usage of "altbootcmd" the "upgrade_available" variable is |
| 46 | used. |
| 47 | If "upgrade_available" is 0, "bootcount" is not saved, if "upgrade_available" is |
| 48 | 1 "bootcount" is save. |
| 49 | So the Userspace Application must set the "upgrade_available" and "bootcount" |
| 50 | variables to 0, if a boot was successfully. |
| 51 | This also prevents writes on all reboots. |