diff options
Diffstat (limited to 'doc/develop/bootstd.rst')
| -rw-r--r-- | doc/develop/bootstd.rst | 34 |
1 files changed, 29 insertions, 5 deletions
diff --git a/doc/develop/bootstd.rst b/doc/develop/bootstd.rst index c47de27..6172dc9 100644 --- a/doc/develop/bootstd.rst +++ b/doc/develop/bootstd.rst @@ -464,6 +464,28 @@ ready File was loaded and is ready for use. In this state the bootflow is ======= ======================================================================= +Migrating from distro_boot +-------------------------- + +To migrate from distro_boot: + +#. Update your board header files to remove the BOOTENV and BOOT_TARGET_xxx + defines. Standard boot finds available boot devices automatically. + +#. Remove the "boot_targets" variable unless you need it. Standard boot uses a + default order from fastest to slowest, which generally matches the order used + by boards. + +#. Make sure that CONFIG_BOOTSTD_DEFAULTS is enabled by your board, so it can + boot common Linux distributions. + +An example patch is at migrate_patch_. + +If you are using custom boot scripts for your board, consider creating your +own bootmeth to hold the logic. There are various examples at +`boot/bootmeth_...`. + + Theory of operation ------------------- @@ -683,11 +705,12 @@ Assuming the bootmeth is happy, or at least indicates that it is willing to try partition. If that works it tries to detect a file system. If that works then it calls the bootmeth device once more, this time to read the bootflow. -Note: At present a filesystem is needed for the bootmeth to be called on block -devices, simply because we don't have any examples where this is not the case. -This feature can be added as needed. Note that sandbox is a special case, since -in that case the host filesystem can be accessed even though the block device -is NULL. +Note: Normally a filesystem is needed for the bootmeth to be called on block +devices, but bootmeths which don't need that can set the BOOTMETHF_ANY_PART +flag to indicate that they can scan any partition. An example is the ChromiumOS +bootmeth which can store a kernel in a raw partition. Note also that sandbox is +a special case, since in that case the host filesystem can be accessed even +though the block device is NULL. If we take the example of the `bootmeth_extlinux` driver, this call ends up at `extlinux_read_bootflow()`. It has the filesystem ready, so tries various @@ -774,3 +797,4 @@ Other ideas: .. _BootLoaderSpec: http://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/ .. _distro_boot: https://github.com/u-boot/u-boot/blob/master/boot/distro.c .. _bootflow_h: https://github.com/u-boot/u-boot/blob/master/include/bootflow.h +.. _migrate_patch: https://patchwork.ozlabs.org/project/uboot/patch/20230727215433.578830-2-sjg@chromium.org/ |