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Experimental: U-Boot versions without BOOTLIMIT support

Some older versions of U-Boot do not have support for the BOOTLIMIT feature, which Mender depends on. In this experimental section we provide a way to work around this missing feature by using custom boot code to simulate the feature. It is equivalent in terms of functionality and robustness.

This section assumes that you are using a custom fork of U-Boot.

The cross platform part

The cross platform bit is actually quite easy, just need to enable the patch for Mender's generic boot code that we already provide. Add this to your u-boot-my-fork.bb or u-boot-my-fork.bbappend file (adjust paths as necessary):

FILESEXTRAPATHS_prepend := "${THISDIR}/../../../meta-mender-core/recipes-bsp/u-boot/patches/experimental:"
SRC_URI_append = " file://0001-Generic-bootlimit-patch-without-U-Boot-boot-counter-.patch"

The board specific part

The board specific part will need customizations specific to your board, but the changes are relatively simple.

  1. The first thing you need to do is to make sure that the board supports the setexpr command in the U-Boot scripting language. This will need the CONFIG_CMD_SETEXPR define to be set inside the board configuration in include/configs.

  2. Second, any existing CONFIG_BOOTCOUNT_LIMIT and/or CONFIG_BOOTCOUNT_ENV defines in the configuration must be removed.

For an example, take a look at the patch provided for the vexpress-qemu MACHINE type. You can try this patch by adding this to your u-boot-my-fork.bb or u-boot-my-fork.bbappend file:

FILESEXTRAPATHS_prepend := "${THISDIR}/../../../meta-mender-qemu/recipes-bsp/u-boot/patches/experimental:"
SRC_URI_append_vexpress-qemu = " file://0002-Enable-custom-bootlimit-code-for-vexpress-qemu.patch"

Obviously this will require using the vexpress-qemu MACHINE type; it will not work on another board.