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@@ -1,239 +1,177 @@
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-Running U-Boot from coreboot on Chromebooks
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-===========================================
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+Chromium OS Support in U-Boot
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+=============================
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-U-Boot can be used as a secondary boot loader in a few situations such as from
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-UEFI and coreboot (see README.x86). Recent Chromebooks use coreboot even on
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-ARM platforms to start up the machine.
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+Introduction
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+------------
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-This document aims to provide a guide to booting U-Boot on a Chromebook. It
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-is only a starting point, and there are many guides on the interwebs. But
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-placing this information in the U-Boot tree should make it easier to find for
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-those who use U-Boot habitually.
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+This describes how to use U-Boot with Chromium OS. Several options are
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+available:
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-Most of these platforms are supported by U-Boot natively, but it is risky to
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-replace the ROM unless you have a servo board and cable to restore it with.
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+ - Running U-Boot from the 'altfw' feature, which is available on selected
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+ Chromebooks from 2019 onwards (initially Grunt). Press '1' from the
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+ developer-mode screen to get into U-Boot. See here for details:
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+ https://sites.google.com/a/chromium.org/dev/chromium-os/poking-around-your-chrome-os-device?pli=1
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+ - Running U-Boot from the disk partition. This involves signing U-Boot and
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+ placing it on the disk, for booting as a 'kernel'. See
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+ README.chromium-chainload for information on this. This is the only
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+ option on non-U-Boot Chromebooks from 2013 to 2018 and is somewhat
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+ more involved.
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-For all of these the standard U-Boot build instructions apply. For example on
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-ARM:
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+ - Running U-Boot with Chromium OS verified boot. This allows U-Boot to be
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+ used instead of either or both of depthcharge (a bootloader which forked
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+ from U-Boot in 2013) and coreboot. See below for more information on
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+ this.
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- sudo apt install gcc-arm-linux-gnueabi
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- mkdir b
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- make O=b/nyan_big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all
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-You can obtain the vbutil_kernel utility here:
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+U-Boot with Chromium OS verified boot
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+-------------------------------------
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- https://drive.google.com/open?id=0B7WYZbZ9zd-3dHlVVXo4VXE2T0U
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+To obtain:
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+ git clone https://github.com/sglass68/u-boot.git
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+ cd u-boot
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+ git checkout cros-master
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-Snow (Samsung ARM Chromebook)
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------------------------------
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+To build for sandbox:
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-See here:
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+ UB=/tmp/b/chromeos_sandbox # U-Boot build directory
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+ CROS=/home/sglass/cosarm # Chromium OS directory
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+ make O=$UB/chromeos_sandbox_defconfig
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+ make O=$UB -j20 -s VBOOT_SOURCE=$CROS/src/platform/vboot_reference \
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+ MAKEFLAGS_VBOOT=DEBUG=1 QUIET=1
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-https://www.chromium.org/chromium-os/firmware-porting-guide/using-nv-u-boot-on-the-samsung-arm-chromebook
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+Replace sandbox with another supported target.
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+This produces $UB/image.bin which contains the firmware binaries in a SPI
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+flash image.
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-Nyan-big
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---------
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-
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-Compiled based on information here:
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-https://lists.denx.de/pipermail/u-boot/2015-March/209530.html
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-https://git.collabora.com/cgit/user/tomeu/u-boot.git/commit/?h=nyan-big
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-https://lists.denx.de/pipermail/u-boot/2017-May/289491.html
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-https://github.com/chromeos-nvidia-androidtv/gnu-linux-on-acer-chromebook-13#copy-data-to-the-sd-card
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-
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-1. Build U-Boot
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-
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- mkdir b
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- make -j8 O=b/nyan-big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all
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-
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-
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-2. Select a .its file
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-
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-Select something from doc/chromium which matches your board, or create your
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-own.
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-
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-Note that the device tree node is required, even though it is not actually
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-used by U-Boot. This is because the Chromebook expects to pass it to the
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-kernel, and crashes if it is not present.
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-
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-
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-3. Build and sign an image
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-
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- ./b/nyan-big/tools/mkimage -f doc/chromium/nyan-big.its u-boot-chromium.fit
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- echo test >dummy.txt
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- vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \
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- --signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \
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- --version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \
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- --bootloader dummy.txt --pack u-boot.kpart
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-
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-
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-4. Prepare an SD card
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-
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- DISK=/dev/sdc # Replace with your actual SD card device
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- sudo cgpt create $DISK
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- sudo cgpt add -b 34 -s 32768 -P 1 -S 1 -t kernel $DISK
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- sudo cgpt add -b 32802 -s 2000000 -t rootfs $DISK
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- sudo gdisk $DISK # Enter command 'w' to write a protective MBR to the disk
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-
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-
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-5. Write U-Boot to the SD card
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+To run on sandbox:
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- sudo dd if=u-boot.kpart of=/dev/sdc1; sync
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+ $UB/tpl/u-boot-tpl -d $UB/u-boot.dtb.out \
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+ -L6 -c "host bind 0 $CROS/src/build/images/cheza/latest/chromiumos_image.bin; vboot go auto" \
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+ -l -w -s state.dtb -r
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+To run on other boards:
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+ Install image.bin in the SPI flash of your device
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+ Boot your system
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-6. Start it up
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-Reboot the device in dev mode. Make sure that you have USB booting enabled. To
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-do this, login as root (via Ctrl-Alt-forward_arrow) and type
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-'enable_dev_usb_boot'. You only need to do this once.
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+Sandbox
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+-------
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-Reboot the device with the SD card inserted. Press Clrl-U at the developer
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-mode screen. It should show something like the following on the display:
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+Most Chromium OS development with U-Boot is undertaken using sandbox. There is
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+a sandbox target available (chromeos_sandbox) which allows running U-Boot on
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+a Linux machine completion with emulations of the display, TPM, disk, etc.
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- U-Boot 2017.07-00637-g242eb42-dirty (May 22 2017 - 06:14:21 -0600)
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+Running sandbox starts TPL, which contains the first phase of vboot, providing
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+a device tree and binding a Chromium OS disk image for use to find kernels
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+(any Chromium OS image will do). It also saves driver state between U-Boot
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+phases into state.dtb and will automatically ensure that memory is shared
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+between all phases. TPL will jump to SPL and then on to U-Boot proper.
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- Model: Acer Chromebook 13 CB5-311
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- Board: Google/NVIDIA Nyan-big, ID: 1
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+It is possible to run with debugging on, e.g.
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- Net: No ethernet found.
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- Hit any key to stop autoboot: 0
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- Tegra124 (Nyan-big) #
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+ gdb --args $UB/tpl/u-boot-tpl -d ....
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+Breakpoints can be set in any U-Boot phase. Overall this is a good debugging
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+environment for new verified-boot features.
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-7. Known problems
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-On the serial console the word MMC is chopped at the start of the line:
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+Samus
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+-----
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-C: sdhci@700b0000: 2, sdhci@700b0400: 1, sdhci@700b0600: 0
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+Basic support is available for samus, using the chromeos_samus target. If you
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+have an em100, use:
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-This is likely due to some problem with change-over of the serial driver
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-during relocation (or perhaps updating the clock setup in board_init()).
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+ sudo em100 -s -c W25Q128FW -d $UB/image.bin -t -r
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+to write the image and then boot samus (Power-Refresh).
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-9. Notes
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-To check that you copied the u-boot.its file correctly, use these commands.
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-You should see that the data at 0x100 in u-boot-chromium.fit is the first few
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-bytes of U-Boot:
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+Boot flow
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+---------
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- hd u-boot-chromium.fit |head -20
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- ...
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- 00000100 b8 00 00 ea 14 f0 9f e5 14 f0 9f e5 14 f0 9f e5 |................|
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+Verified boot starts in TPL, which selects the A or B SPL, which in turn selects
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+the A or B U-Boot. Then this jumps to the selected kernel. If anything goes
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+wrong, the device reboots and the recovery SPL and U-Boot are used instead.
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- hd b/nyan-big/u-boot.bin |head
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- 00000000 b8 00 00 ea 14 f0 9f e5 14 f0 9f e5 14 f0 9f e5 |................|
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+More details are available here:
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+ https://www.chromium.org/chromium-os/chromiumos-design-docs/firmware-boot-and-recovery
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-The 'data' property of the FIT is set up to start at offset 0x100 bytes into
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-the file. The change to CONFIG_SYS_TEXT_BASE is also an offset of 0x100 bytes
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-from the load address. If this changes, you either need to modify U-Boot to be
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-fully relocatable, or expect it to hang.
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+New uclasses
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+------------
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-chromebook_jerry
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-----------------
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+Several uclasses are provided in cros/:
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-The instruction are similar to those for Nyan with changes as noted below:
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+ UCLASS_CROS_AUX_FW Chrome OS auxiliary firmware
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+ UCLASS_CROS_FWSTORE Chrome OS firmware storage
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+ UCLASS_CROS_NVDATA Chrome OS non-volatile data device
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+ UCLASS_CROS_VBOOT_EC Chrome OS vboot EC operations
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+ UCLASS_CROS_VBOOT_FLAG Chrome OS verified boot flag
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-1. Patch U-Boot
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+The existing UCLASS_CROS_EC is also used.
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-Open include/configs/rk3288_common.h
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-Change:
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-
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-#define CONFIG_SYS_TEXT_BASE 0x00100000
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-
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-to:
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-
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-#define CONFIG_SYS_TEXT_BASE 0x02000100
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-
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-
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-
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-2. Build U-Boot
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-
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- mkdir b
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- make -j8 O=b/chromebook_jerry CROSS_COMPILE=arm-linux-gnueabi- \
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- chromebook_jerry_defconfig all
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-
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-
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-3. See above
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-
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-4. Build and sign an image
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-
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- ./b/chromebook_jerry/tools/mkimage -f doc/chromium/chromebook_jerry.its \
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- u-boot-chromium.fit
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- echo test >dummy.txt
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- vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \
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- --signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \
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- --version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \
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- --bootloader dummy.txt --pack u-boot.kpart
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-
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-
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-5. See above
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+Commands
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+--------
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-6. See above
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+A new 'vboot' command is provided to run particular vboot stages. The most
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+useful command is 'vboot go auto', which continues where the last stage left
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+off.
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-7. Start it up
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+Note that TPL and SPL do not supports commands as yet, so the vboot code is
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+called directly from the SPL boot devices (BOOT_DEVICE_CROS_VBOOT). See
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+cros_load_image_tpl() and cros_load_image_spl() which both call
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+vboot_run_auto().
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-Reboot the device in dev mode. Make sure that you have USB booting enabled. To
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-do this, login as root (via Ctrl-Alt-forward_arrow) and type
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-'enable_dev_usb_boot'. You only need to do this once.
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-Reboot the device with the SD card inserted. Press Clrl-U at the developer
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-mode screen. It should show something like the following on the display:
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+Config options
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+--------------
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- U-Boot 2017.05-00649-g72acdbf-dirty (May 29 2017 - 14:57:05 -0600)
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+The main option is CONFIG_CHROMEOS, which enables a wide array of other options
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+so that the required features are present.
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- Model: Google Jerry
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- Net: Net Initialization Skipped
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- No ethernet found.
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- Hit any key to stop autoboot: 0
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+Device-tree config
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+------------------
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-8. Known problems
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+Various options are available which control the operation of verified boot.
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+See cros/dts/bindings/config.txt for details. Most config is handled at run-
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+time, although build-time config (with Kconfig) could also be added fairly
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+easily.
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-None as yet.
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+Porting to other hardware
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+-------------------------
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-9. Notes
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+A basic port to samus (Chromebook Pixel 2015) is in a basic working state,
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+using the chromeos_samus target. Patches will likely be forthcoming in early
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+2019. Ports to an ARM board and coreboot (for x86 Chromebooks) are in the
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+dreaming state.
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-None as yet.
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+Tests
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+-----
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-Other notes
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-===========
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+Chromium OS firmware has a very limited set of tests. The tests that originally
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+existed in U-Boot were not brought over to coreboot or depthcharge.
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-flashrom
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---------
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+The U-Boot tests ('make check') do operate, but at present there are no
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+Chromium OS tests available. These will hopefully come together over time. Of
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+course the above sandbox feature provides a sort of functional test and can
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+detecte problems that affect the flow or particular vboot features.
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- Used to make a backup of your firmware, or to replace it.
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- See: https://www.chromium.org/chromium-os/packages/cros-flashrom
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+TO DO
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+-----
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+- Support for booting from coreboot (patches expected March 2019)
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+- Support for booting from an ARM board, e.g. bob
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-coreboot
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---------
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-Coreboot itself is not designed to actually boot an OS. Instead, a program
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-called Depthcharge is used. This originally came out of U-Boot and was then
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-heavily hacked and modified such that is is almost unrecognisable. It does
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-include a very small part of the U-Boot command-line interface but is not
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-usable as a general-purpose boot loader.
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-
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-In addition, it has a very unusual design in that it does not do device init
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-itself, but instead relies on coreboot. This is similar to (in U-Boot) having
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-a SPI driver with an empty probe() method, relying on whatever was set up
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-beforehand. It can be quite hard to figure out between these two code bases
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-what settings are actually used. When chain-loading into U-Boot we must be
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-careful to reinit anything that U-Boot expects. If not, some peripherals (or
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-the whole machine) may not work. This makes the process of chainloading more
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-complicated than it could be on some platforms.
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-
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-Finally, it supports only a subset of the U-Boot's FIT format. In particular
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-it uses a fixed address to load the FIT and does not support load/exec
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-addresses. This means that U-Boot must be able to boot from whatever
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-address Depthcharge happens to use (it is the CONFIG_KERNEL_START setting
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-in Depthcharge). In practice this means that the data in the kernel@1 FIT node
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-(see above) must start at the same address as U-Boot's CONFIG_SYS_TEXT_BASE.
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+Simon Glass
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+sjg@chromium.org
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+7 October 2018
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