From: Simon Glass Date: Wed, 17 Jul 2024 08:30:57 +0000 (+0100) Subject: doc: Add a description for bootmeth_cros X-Git-Url: http://git.dujemihanovic.xyz/contact?a=commitdiff_plain;h=56418511e9fd5ca34c38c896a364ea0249c53610;p=u-boot.git doc: Add a description for bootmeth_cros Add documentation for the cros bootmeth. Signed-off-by: Simon Glass Reviewed-by: Quentin Schulz Reviewed-by: Mattijs Korpershoek --- diff --git a/doc/develop/bootstd/cros.rst b/doc/develop/bootstd/cros.rst new file mode 100644 index 0000000000..85af10588c --- /dev/null +++ b/doc/develop/bootstd/cros.rst @@ -0,0 +1,33 @@ +.. SPDX-License-Identifier: GPL-2.0+: + +ChromiumOS Bootmeth +=================== + +ChromiumOS provides a mechanism for booting its Operating System from a block +device, described +`here `_. + +U-Boot includes support for reading the associated data structures from the +device and identifying a bootable ChromiumOS image. This structure includes the +kernel itself, boot arguments (kernel command line), as well as the x86 setup +block (for x86 only). + +When invoked on a bootdev, this bootmeth searches for kernel partitions with +the appropriate GUID (Globally Unique Identifier). When found, the information +is loaded and a bootflow is created. + +When the bootflow is booted, the bootmeth reads the kernel and boot arguments. +It then boots the kernel using zboot (on x86) or bootm (on ARM). The boot +arguments are adjusted to replace `%U` with the UUID of the selected kernel +partition. This results in the correct root disk being used, which is the next +partition after the kernel partition. + +For ARM, a :doc:`/usage/fit/index` is used. The `CONFIG_FIT_BEST_MATCH` option +must be enabled for U-Boot to select the correct devicetree to boot with. + +Note that a ChromiumOS image typically has two copies of the Operating System, +each with its own kernel and root disk. There is no initial ramdisk (initrd). +This means that this bootmeth typically locates two separate images. + +The compatible string "u-boot,cros" is used for the driver. It is present +if `CONFIG_BOOTMETH_CROS` is enabled. diff --git a/doc/develop/bootstd/index.rst b/doc/develop/bootstd/index.rst index f8fce7207c..69fd3c2d2e 100644 --- a/doc/develop/bootstd/index.rst +++ b/doc/develop/bootstd/index.rst @@ -10,3 +10,4 @@ Standard Boot extlinux pxelinux qfw + cros diff --git a/doc/develop/bootstd/overview.rst b/doc/develop/bootstd/overview.rst index ef878963c9..de15fa41a1 100644 --- a/doc/develop/bootstd/overview.rst +++ b/doc/develop/bootstd/overview.rst @@ -421,6 +421,7 @@ Bootmeth drivers are provided for booting from various media: - U-Boot scripts from disk, network or SPI flash - EFI boot using bootefi from disk - VBE + - :doc:`ChromiumOS ` ChromiumOS boot from a disk - EFI boot using boot manager - Android bootflow (boot image v4) - :doc:`QFW `: QEMU firmware interface