mirror of
https://github.com/brain-hackers/u-boot-brain
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![Atish Patra](/assets/img/avatar_default.png)
Add compressed Image parsing support so that booti can parse both flat and compressed Image to boot Linux. Currently, it is difficult to calculate a safe address for every board where the compressed image can be decompressed. It is also not possible to figure out the size of the compressed file as well. Thus, user need to set two additional environment variables kernel_comp_addr_r and filesize to make this work. Following compression methods are supported for now. lzma, lzo, bzip2, gzip. lz4 support is not added as ARM64 kernel generates a lz4 compressed image with legacy header which U-Boot doesn't know how to parse and decompress. Tested on HiFive Unleashed and Qemu for RISC-V. Tested on Qemu for ARM64. Signed-off-by: Atish Patra <atish.patra@wdc.com> Reviewed-by: Tom Rini <trini@konsulko.com> [trini: Fix minor rST formatting problems] Signed-off-by: Tom Rini <trini@konsulko.com>
420 lines
17 KiB
Plaintext
420 lines
17 KiB
Plaintext
SPDX-License-Identifier: GPL-2.0+
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/*
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* (C) Copyright 2014 Red Hat Inc.
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* Copyright (c) 2014-2015, NVIDIA CORPORATION. All rights reserved.
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* Copyright (C) 2015 K. Merker <merker@debian.org>
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*/
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Generic Distro Configuration Concept
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====================================
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Linux distributions are faced with supporting a variety of boot mechanisms,
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environments or bootloaders (PC BIOS, EFI, U-Boot, Barebox, ...). This makes
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life complicated. Worse, bootloaders such as U-Boot have a configurable set
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of features, and each board chooses to enable a different set of features.
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Hence, distros typically need to have board-specific knowledge in order to
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set up a bootable system.
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This document defines a common set of U-Boot features that are required for
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a distro to support the board in a generic fashion. Any board wishing to
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allow distros to install and boot in an out-of-the-box fashion should enable
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all these features. Linux distros can then create a single set of boot
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support/install logic that targets these features. This will allow distros
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to install on many boards without the need for board-specific logic.
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In fact, some of these features can be implemented by any bootloader, thus
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decoupling distro install/boot logic from any knowledge of the bootloader.
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This model assumes that boards will load boot configuration files from a
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regular storage mechanism (eMMC, SD card, USB Disk, SATA disk, etc.) with
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a standard partitioning scheme (MBR, GPT). Boards that cannot support this
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storage model are outside the scope of this document, and may still need
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board-specific installer/boot-configuration support in a distro.
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To some extent, this model assumes that a board has a separate boot flash
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that contains U-Boot, and that the user has somehow installed U-Boot to this
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flash before running the distro installer. Even on boards that do not conform
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to this aspect of the model, the extent of the board-specific support in the
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distro installer logic would be to install a board-specific U-Boot package to
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the boot partition during installation. This distro-supplied U-Boot can still
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implement the same features as on any other board, and hence the distro's boot
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configuration file generation logic can still be board-agnostic.
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Locating Bootable Disks
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-----------------------
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Typical desktop/server PCs search all (or a user-defined subset of) attached
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storage devices for a bootable partition, then load the bootloader or boot
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configuration files from there. A U-Boot board port that enables the features
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mentioned in this document will search for boot configuration files in the
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same way.
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Thus, distros do not need to manipulate any kind of bootloader-specific
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configuration data to indicate which storage device the system should boot
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from.
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Distros simply need to install the boot configuration files (see next
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section) in an ext2/3/4 or FAT partition, mark the partition bootable (via
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the MBR bootable flag, or GPT legacy_bios_bootable attribute), and U-Boot (or
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any other bootloader) will find those boot files and execute them. This is
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conceptually identical to creating a grub2 configuration file on a desktop
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PC.
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Note that in the absence of any partition that is explicitly marked bootable,
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U-Boot falls back to searching the first valid partition of a disk for boot
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configuration files. Other bootloaders are recommended to do the same, since
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I believe that partition table bootable flags aren't so commonly used outside
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the realm of x86 PCs.
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U-Boot can also search for boot configuration files from a TFTP server.
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Boot Configuration Files
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------------------------
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The standard format for boot configuration files is that of extlinux.conf, as
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handled by U-Boot's "syslinux" (disk) or "pxe boot" (network). This is roughly
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as specified at:
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http://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/
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... with the exceptions that the BootLoaderSpec document:
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* Prescribes a separate configuration per boot menu option, whereas U-Boot
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lumps all options into a single extlinux.conf file. Hence, U-Boot searches
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for /extlinux/extlinux.conf then /boot/extlinux/extlinux.conf on disk, or
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pxelinux.cfg/default over the network.
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* Does not document the fdtdir option, which automatically selects the DTB to
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pass to the kernel.
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One example extlinux.conf generated by the Fedora installer is:
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------------------------------------------------------------
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# extlinux.conf generated by anaconda
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ui menu.c32
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menu autoboot Welcome to Fedora. Automatic boot in # second{,s}. Press a key for options.
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menu title Fedora Boot Options.
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menu hidden
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timeout 50
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#totaltimeout 9000
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default Fedora (3.17.0-0.rc4.git2.1.fc22.armv7hl+lpae) 22 (Rawhide)
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label Fedora (3.17.0-0.rc4.git2.1.fc22.armv7hl) 22 (Rawhide)
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kernel /boot/vmlinuz-3.17.0-0.rc4.git2.1.fc22.armv7hl
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append ro root=UUID=8eac677f-8ea8-4270-8479-d5ddbb797450 console=ttyS0,115200n8 LANG=en_US.UTF-8 drm.debug=0xf
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fdtdir /boot/dtb-3.17.0-0.rc4.git2.1.fc22.armv7hl
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initrd /boot/initramfs-3.17.0-0.rc4.git2.1.fc22.armv7hl.img
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label Fedora (3.17.0-0.rc4.git2.1.fc22.armv7hl+lpae) 22 (Rawhide)
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kernel /boot/vmlinuz-3.17.0-0.rc4.git2.1.fc22.armv7hl+lpae
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append ro root=UUID=8eac677f-8ea8-4270-8479-d5ddbb797450 console=ttyS0,115200n8 LANG=en_US.UTF-8 drm.debug=0xf
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fdtdir /boot/dtb-3.17.0-0.rc4.git2.1.fc22.armv7hl+lpae
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initrd /boot/initramfs-3.17.0-0.rc4.git2.1.fc22.armv7hl+lpae.img
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label Fedora-0-rescue-8f6ba7b039524e0eb957d2c9203f04bc (0-rescue-8f6ba7b039524e0eb957d2c9203f04bc)
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kernel /boot/vmlinuz-0-rescue-8f6ba7b039524e0eb957d2c9203f04bc
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initrd /boot/initramfs-0-rescue-8f6ba7b039524e0eb957d2c9203f04bc.img
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append ro root=UUID=8eac677f-8ea8-4270-8479-d5ddbb797450 console=ttyS0,115200n8
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fdtdir /boot/dtb-3.16.0-0.rc6.git1.1.fc22.armv7hl+lpae
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------------------------------------------------------------
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Another hand-crafted network boot configuration file is:
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------------------------------------------------------------
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TIMEOUT 100
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MENU TITLE TFTP boot options
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LABEL jetson-tk1-emmc
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MENU LABEL ../zImage root on Jetson TK1 eMMC
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LINUX ../zImage
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FDTDIR ../
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APPEND console=ttyS0,115200n8 console=tty1 loglevel=8 rootwait rw earlyprintk root=PARTUUID=80a5a8e9-c744-491a-93c1-4f4194fd690b
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LABEL venice2-emmc
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MENU LABEL ../zImage root on Venice2 eMMC
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LINUX ../zImage
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FDTDIR ../
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APPEND console=ttyS0,115200n8 console=tty1 loglevel=8 rootwait rw earlyprintk root=PARTUUID=5f71e06f-be08-48ed-b1ef-ee4800cc860f
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LABEL sdcard
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MENU LABEL ../zImage, root on 2GB sdcard
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LINUX ../zImage
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FDTDIR ../
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APPEND console=ttyS0,115200n8 console=tty1 loglevel=8 rootwait rw earlyprintk root=PARTUUID=b2f82cda-2535-4779-b467-094a210fbae7
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LABEL fedora-installer-fk
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MENU LABEL Fedora installer w/ Fedora kernel
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LINUX fedora-installer/vmlinuz
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INITRD fedora-installer/initrd.img.orig
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FDTDIR fedora-installer/dtb
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APPEND loglevel=8 ip=dhcp inst.repo=http://10.0.0.2/mirrors/fedora/linux/development/rawhide/armhfp/os/ rd.shell cma=64M
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------------------------------------------------------------
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U-Boot Implementation
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=====================
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Enabling the distro options
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---------------------------
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In your board's defconfig, enable the DISTRO_DEFAULTS option by adding
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a line with "CONFIG_DISTRO_DEFAULTS=y". If you want to enable this
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from Kconfig itself, for e.g. all boards using a specific SoC then
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add a "imply DISTRO_DEFAULTS" to your SoC CONFIG option.
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In your board configuration file, include the following:
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------------------------------------------------------------
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#ifndef CONFIG_SPL_BUILD
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#include <config_distro_bootcmd.h>
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#endif
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------------------------------------------------------------
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The first of those headers primarily enables a core set of U-Boot features,
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such as support for MBR and GPT partitions, ext* and FAT filesystems, booting
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raw zImage and initrd (rather than FIT- or uImage-wrapped files), etc. Network
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boot support is also enabled here, which is useful in order to boot distro
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installers given that distros do not commonly distribute bootable install
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media for non-PC targets at present.
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Finally, a few options that are mostly relevant only when using U-Boot-
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specific boot.scr scripts are enabled. This enables distros to generate a
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U-Boot-specific boot.scr script rather than extlinux.conf as the boot
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configuration file. While doing so is fully supported, and
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CONFIG_DISTRO_DEFAULTS exposes enough parameterization to boot.scr to
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allow for board-agnostic boot.scr content, this document recommends that
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distros generate extlinux.conf rather than boot.scr. extlinux.conf is intended
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to work across multiple bootloaders, whereas boot.scr will only work with
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U-Boot. TODO: document the contract between U-Boot and boot.scr re: which
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environment variables a generic boot.scr may rely upon.
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The second of those headers sets up the default environment so that $bootcmd
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is defined in a way that searches attached disks for boot configuration files,
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and executes them if found.
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Required Environment Variables
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------------------------------
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The U-Boot "syslinux" and "pxe boot" commands require a number of environment
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variables be set. Default values for these variables are often hard-coded into
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CONFIG_EXTRA_ENV_SETTINGS in the board's U-Boot configuration file, so that
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the user doesn't have to configure them.
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fdt_addr:
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Mandatory for any system that provides the DTB in HW (e.g. ROM) and wishes
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to pass that DTB to Linux, rather than loading a DTB from the boot
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filesystem. Prohibited for any other system.
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If specified a DTB to boot the system must be available at the given
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address.
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fdt_addr_r:
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Mandatory. The location in RAM where the DTB will be loaded or copied to when
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processing the fdtdir/devicetreedir or fdt/devicetree options in
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extlinux.conf.
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This is mandatory even when fdt_addr is provided, since extlinux.conf must
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always be able to provide a DTB which overrides any copy provided by the HW.
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A size of 1MB for the FDT/DTB seems reasonable.
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ramdisk_addr_r:
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Mandatory. The location in RAM where the initial ramdisk will be loaded to
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when processing the initrd option in extlinux.conf.
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It is recommended that this location be highest in RAM out of fdt_addr_,
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kernel_addr_r, and ramdisk_addr_r, so that the RAM disk can vary in size
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and use any available RAM.
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kernel_addr_r:
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Mandatory. The location in RAM where the kernel will be loaded to when
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processing the kernel option in the extlinux.conf.
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The kernel should be located within the first 128M of RAM in order for the
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kernel CONFIG_AUTO_ZRELADDR option to work, which is likely enabled on any
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distro kernel. Since the kernel will decompress itself to 0x8000 after the
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start of RAM, kernel_addr_r should not overlap that area, or the kernel will
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have to copy itself somewhere else first before decompression.
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A size of 16MB for the kernel is likely adequate.
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kernel_comp_addr_r:
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Optional. This is only required if user wants to boot Linux from a compressed
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Image(.gz, .bz2, .lzma, .lzo) using booti command. It represents the location
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in RAM where the compressed Image will be decompressed temporarily. Once the
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decompression is complete, decompressed data will be moved kernel_addr_r for
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booting.
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kernel_comp_size:
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Optional. This is only required if user wants to boot Linux from a compressed
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Image using booti command. It represents the size of the compressed file. The
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size has to at least the size of loaded image for decompression to succeed.
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pxefile_addr_r:
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Mandatory. The location in RAM where extlinux.conf will be loaded to prior
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to processing.
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A size of 1MB for extlinux.conf is more than adequate.
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scriptaddr:
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Mandatory, if the boot script is boot.scr rather than extlinux.conf. The
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location in RAM where boot.scr will be loaded to prior to execution.
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A size of 1MB for extlinux.conf is more than adequate.
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For suggestions on memory locations for ARM systems, you must follow the
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guidelines specified in Documentation/arm/Booting in the Linux kernel tree.
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For a commented example of setting these values, please see the definition of
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MEM_LAYOUT_ENV_SETTINGS in include/configs/tegra124-common.h.
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Boot Target Configuration
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-------------------------
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<config_distro_bootcmd.h> defines $bootcmd and many helper command variables
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that automatically search attached disks for boot configuration files and
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execute them. Boards must provide configure <config_distro_bootcmd.h> so that
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it supports the correct set of possible boot device types. To provide this
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configuration, simply define macro BOOT_TARGET_DEVICES prior to including
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<config_distro_bootcmd.h>. For example:
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------------------------------------------------------------
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#ifndef CONFIG_SPL_BUILD
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#define BOOT_TARGET_DEVICES(func) \
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func(MMC, mmc, 1) \
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func(MMC, mmc, 0) \
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func(USB, usb, 0) \
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func(PXE, pxe, na) \
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func(DHCP, dhcp, na)
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#include <config_distro_bootcmd.h>
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#endif
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------------------------------------------------------------
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Each entry in the macro defines a single boot device (e.g. a specific eMMC
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device or SD card) or type of boot device (e.g. USB disk). The parameters to
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the func macro (passed in by the internal implementation of the header) are:
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- Upper-case disk type (MMC, SATA, SCSI, IDE, USB, DHCP, PXE, VIRTIO).
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- Lower-case disk type (same options as above).
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- ID of the specific disk (MMC only) or ignored for other types.
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User Configuration
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==================
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Once the user has installed U-Boot, it is expected that the environment will
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be reset to the default values in order to enable $bootcmd and friends, as set
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up by <config_distro_bootcmd.h>. After this, various environment variables may
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be altered to influence the boot process:
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boot_targets:
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The list of boot locations searched.
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Example: mmc0, mmc1, usb, pxe
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Entries may be removed or re-ordered in this list to affect the boot order.
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boot_prefixes:
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For disk-based booting, the list of directories within a partition that are
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searched for boot configuration files (extlinux.conf, boot.scr).
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Example: / /boot/
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Entries may be removed or re-ordered in this list to affect the set of
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directories which are searched.
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boot_scripts:
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The name of U-Boot style boot.scr files that $bootcmd searches for.
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Example: boot.scr.uimg boot.scr
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(Typically we expect extlinux.conf to be used, but execution of boot.scr is
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maintained for backwards-compatibility.)
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Entries may be removed or re-ordered in this list to affect the set of
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filenames which are supported.
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scan_dev_for_extlinux:
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If you want to disable extlinux.conf on all disks, set the value to something
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innocuous, e.g. setenv scan_dev_for_extlinux true.
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scan_dev_for_scripts:
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If you want to disable boot.scr on all disks, set the value to something
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innocuous, e.g. setenv scan_dev_for_scripts true.
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boot_net_usb_start:
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If you want to prevent USB enumeration by distro boot commands which execute
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network operations, set the value to something innocuous, e.g. setenv
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boot_net_usb_start true. This would be useful if you know your Ethernet
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device is not attached to USB, and you wish to increase boot speed by
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avoiding unnecessary actions.
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boot_net_pci_enum:
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If you want to prevent PCI enumeration by distro boot commands which execute
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network operations, set the value to something innocuous, e.g. setenv
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boot_net_pci_enum true. This would be useful if you know your Ethernet
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device is not attached to PCI, and you wish to increase boot speed by
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avoiding unnecessary actions.
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Interactively booting from a specific device at the u-boot prompt
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=================================================================
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For interactively booting from a user-selected device at the u-boot command
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prompt, the environment provides predefined bootcmd_<target> variables for
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every target defined in boot_targets, which can be run be the user.
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If the target is a storage device, the format of the target is always
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<device type><device number>, e.g. mmc0. Specifying the device number is
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mandatory for storage devices, even if only support for a single instance
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of the storage device is actually implemented.
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For network targets (dhcp, pxe), only the device type gets specified;
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they do not have a device number.
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Examples:
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- run bootcmd_usb0
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boots from the first USB mass storage device
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- run bootcmd_mmc1
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boots from the second MMC device
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- run bootcmd_pxe
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boots by tftp using a pxelinux.cfg
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The list of possible targets consists of:
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- network targets
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* dhcp
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* pxe
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- storage targets (to which a device number must be appended)
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* mmc
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* sata
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* scsi
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* ide
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* usb
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* virtio
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Other *boot* variables than the ones defined above are only for internal use
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of the boot environment and are not guaranteed to exist or work in the same
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way in future u-boot versions. In particular the <device type>_boot
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variables (e.g. mmc_boot, usb_boot) are a strictly internal implementation
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detail and must not be used as a public interface.
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