| Running U-Boot from coreboot on Chromebooks | |
| =========================================== | |
| U-Boot can be used as a secondary boot loader in a few situations such as from | |
| UEFI and coreboot (see README.x86). Recent Chromebooks use coreboot even on | |
| ARM platforms to start up the machine. | |
| This document aims to provide a guide to booting U-Boot on a Chromebook. It | |
| is only a starting point, and there are many guides on the interwebs. But | |
| placing this information in the U-Boot tree should make it easier to find for | |
| those who use U-Boot habitually. | |
| Most of these platforms are supported by U-Boot natively, but it is risky to | |
| replace the ROM unless you have a servo board and cable to restore it with. | |
| For all of these the standard U-Boot build instructions apply. For example on | |
| ARM: | |
| sudo apt install gcc-arm-linux-gnueabi | |
| mkdir b | |
| make O=b/nyan_big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all | |
| You can obtain the vbutil_kernel utility here: | |
| https://drive.google.com/open?id=0B7WYZbZ9zd-3dHlVVXo4VXE2T0U | |
| Snow (Samsung ARM Chromebook) | |
| ----------------------------- | |
| See here: | |
| https://www.chromium.org/chromium-os/firmware-porting-guide/using-nv-u-boot-on-the-samsung-arm-chromebook | |
| Nyan-big | |
| -------- | |
| Compiled based on information here: | |
| https://lists.denx.de/pipermail/u-boot/2015-March/209530.html | |
| https://git.collabora.com/cgit/user/tomeu/u-boot.git/commit/?h=nyan-big | |
| https://lists.denx.de/pipermail/u-boot/2017-May/289491.html | |
| https://github.com/chromeos-nvidia-androidtv/gnu-linux-on-acer-chromebook-13#copy-data-to-the-sd-card | |
| 1. Build U-Boot | |
| mkdir b | |
| make -j8 O=b/nyan-big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all | |
| 2. Select a .its file | |
| Select something from doc/chromium which matches your board, or create your | |
| own. | |
| Note that the device tree node is required, even though it is not actually | |
| used by U-Boot. This is because the Chromebook expects to pass it to the | |
| kernel, and crashes if it is not present. | |
| 3. Build and sign an image | |
| ./b/nyan-big/tools/mkimage -f doc/chromium/nyan-big.its u-boot-chromium.fit | |
| echo test >dummy.txt | |
| vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \ | |
| --signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \ | |
| --version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \ | |
| --bootloader dummy.txt --pack u-boot.kpart | |
| 4. Prepare an SD card | |
| DISK=/dev/sdc # Replace with your actual SD card device | |
| sudo cgpt create $DISK | |
| sudo cgpt add -b 34 -s 32768 -P 1 -S 1 -t kernel $DISK | |
| sudo cgpt add -b 32802 -s 2000000 -t rootfs $DISK | |
| sudo gdisk $DISK # Enter command 'w' to write a protective MBR to the disk | |
| 5. Write U-Boot to the SD card | |
| sudo dd if=u-boot.kpart of=/dev/sdc1; sync | |
| 6. Start it up | |
| Reboot the device in dev mode. Make sure that you have USB booting enabled. To | |
| do this, login as root (via Ctrl-Alt-forward_arrow) and type | |
| 'enable_dev_usb_boot'. You only need to do this once. | |
| Reboot the device with the SD card inserted. Press Clrl-U at the developer | |
| mode screen. It should show something like the following on the display: | |
| U-Boot 2017.07-00637-g242eb42-dirty (May 22 2017 - 06:14:21 -0600) | |
| Model: Acer Chromebook 13 CB5-311 | |
| Board: Google/NVIDIA Nyan-big, ID: 1 | |
| Net: No ethernet found. | |
| Hit any key to stop autoboot: 0 | |
| Tegra124 (Nyan-big) # | |
| 7. Known problems | |
| On the serial console the word MMC is chopped at the start of the line: | |
| C: sdhci@700b0000: 2, sdhci@700b0400: 1, sdhci@700b0600: 0 | |
| This is likely due to some problem with change-over of the serial driver | |
| during relocation (or perhaps updating the clock setup in board_init()). | |
| 9. Notes | |
| To check that you copied the u-boot.its file correctly, use these commands. | |
| You should see that the data at 0x100 in u-boot-chromium.fit is the first few | |
| bytes of U-Boot: | |
| hd u-boot-chromium.fit |head -20 | |
| ... | |
| 00000100 b8 00 00 ea 14 f0 9f e5 14 f0 9f e5 14 f0 9f e5 |................| | |
| hd b/nyan-big/u-boot.bin |head | |
| 00000000 b8 00 00 ea 14 f0 9f e5 14 f0 9f e5 14 f0 9f e5 |................| | |
| The 'data' property of the FIT is set up to start at offset 0x100 bytes into | |
| the file. The change to CONFIG_SYS_TEXT_BASE is also an offset of 0x100 bytes | |
| from the load address. If this changes, you either need to modify U-Boot to be | |
| fully relocatable, or expect it to hang. | |
| chromebook_jerry | |
| ---------------- | |
| The instruction are similar to those for Nyan with changes as noted below: | |
| 1. Patch U-Boot | |
| Open include/configs/rk3288_common.h | |
| Change: | |
| #define CONFIG_SYS_TEXT_BASE 0x00100000 | |
| to: | |
| #define CONFIG_SYS_TEXT_BASE 0x02000100 | |
| 2. Build U-Boot | |
| mkdir b | |
| make -j8 O=b/chromebook_jerry CROSS_COMPILE=arm-linux-gnueabi- \ | |
| chromebook_jerry_defconfig all | |
| 3. See above | |
| 4. Build and sign an image | |
| ./b/chromebook_jerry/tools/mkimage -f doc/chromium/chromebook_jerry.its \ | |
| u-boot-chromium.fit | |
| echo test >dummy.txt | |
| vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \ | |
| --signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \ | |
| --version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \ | |
| --bootloader dummy.txt --pack u-boot.kpart | |
| 5. See above | |
| 6. See above | |
| 7. Start it up | |
| Reboot the device in dev mode. Make sure that you have USB booting enabled. To | |
| do this, login as root (via Ctrl-Alt-forward_arrow) and type | |
| 'enable_dev_usb_boot'. You only need to do this once. | |
| Reboot the device with the SD card inserted. Press Clrl-U at the developer | |
| mode screen. It should show something like the following on the display: | |
| U-Boot 2017.05-00649-g72acdbf-dirty (May 29 2017 - 14:57:05 -0600) | |
| Model: Google Jerry | |
| Net: Net Initialization Skipped | |
| No ethernet found. | |
| Hit any key to stop autoboot: 0 | |
| 8. Known problems | |
| None as yet. | |
| 9. Notes | |
| None as yet. | |
| Other notes | |
| =========== | |
| flashrom | |
| -------- | |
| Used to make a backup of your firmware, or to replace it. | |
| See: https://www.chromium.org/chromium-os/packages/cros-flashrom | |
| coreboot | |
| -------- | |
| Coreboot itself is not designed to actually boot an OS. Instead, a program | |
| called Depthcharge is used. This originally came out of U-Boot and was then | |
| heavily hacked and modified such that is is almost unrecognisable. It does | |
| include a very small part of the U-Boot command-line interface but is not | |
| usable as a general-purpose boot loader. | |
| In addition, it has a very unusual design in that it does not do device init | |
| itself, but instead relies on coreboot. This is similar to (in U-Boot) having | |
| a SPI driver with an empty probe() method, relying on whatever was set up | |
| beforehand. It can be quite hard to figure out between these two code bases | |
| what settings are actually used. When chain-loading into U-Boot we must be | |
| careful to reinit anything that U-Boot expects. If not, some peripherals (or | |
| the whole machine) may not work. This makes the process of chainloading more | |
| complicated than it could be on some platforms. | |
| Finally, it supports only a subset of the U-Boot's FIT format. In particular | |
| it uses a fixed address to load the FIT and does not support load/exec | |
| addresses. This means that U-Boot must be able to boot from whatever | |
| address Depthcharge happens to use (it is the CONFIG_KERNEL_START setting | |
| in Depthcharge). In practice this means that the data in the kernel@1 FIT node | |
| (see above) must start at the same address as U-Boot's CONFIG_SYS_TEXT_BASE. |