1Running U-Boot from coreboot on Chromebooks 2=========================================== 3 4U-Boot can be used as a secondary boot loader in a few situations such as from 5UEFI and coreboot (see README.x86). Recent Chromebooks use coreboot even on 6ARM platforms to start up the machine. 7 8This document aims to provide a guide to booting U-Boot on a Chromebook. It 9is only a starting point, and there are many guides on the interwebs. But 10placing this information in the U-Boot tree should make it easier to find for 11those who use U-Boot habitually. 12 13Most of these platforms are supported by U-Boot natively, but it is risky to 14replace the ROM unless you have a servo board and cable to restore it with. 15 16 17For all of these the standard U-Boot build instructions apply. For example on 18ARM: 19 20 sudo apt install gcc-arm-linux-gnueabi 21 mkdir b 22 make O=b/nyan_big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all 23 24You can obtain the vbutil_kernel utility here: 25 26 https://drive.google.com/open?id=0B7WYZbZ9zd-3dHlVVXo4VXE2T0U 27 28 29Snow (Samsung ARM Chromebook) 30----------------------------- 31 32See here: 33 34https://www.chromium.org/chromium-os/firmware-porting-guide/using-nv-u-boot-on-the-samsung-arm-chromebook 35 36 37Nyan-big 38-------- 39 40Compiled based on information here: 41https://lists.denx.de/pipermail/u-boot/2015-March/209530.html 42https://git.collabora.com/cgit/user/tomeu/u-boot.git/commit/?h=nyan-big 43https://lists.denx.de/pipermail/u-boot/2017-May/289491.html 44https://github.com/chromeos-nvidia-androidtv/gnu-linux-on-acer-chromebook-13#copy-data-to-the-sd-card 45 461. Patch U-Boot 47 48Open include/configs/tegra124-common.h 49 50Change: 51 52#define CONFIG_SYS_TEXT_BASE 0x80110000 53 54to: 55 56#define CONFIG_SYS_TEXT_BASE 0x81000100 57 58 592. Build U-Boot 60 61 mkdir b 62 make -j8 O=b/nyan-big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all 63 64 653. Select a .its file 66 67Select something from doc/chromium which matches your board, or create your 68own. 69 70Note that the device tree node is required, even though it is not actually 71used by U-Boot. This is because the Chromebook expects to pass it to the 72kernel, and crashes if it is not present. 73 74 754. Build and sign an image 76 77 ./b/nyan-big/tools/mkimage -f doc/chromium/nyan-big.its u-boot-chromium.fit 78 echo test >dummy.txt 79 vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \ 80 --signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \ 81 --version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \ 82 --bootloader dummy.txt --pack u-boot.kpart 83 84 855. Prepare an SD card 86 87 DISK=/dev/sdc # Replace with your actual SD card device 88 sudo cgpt create $DISK 89 sudo cgpt add -b 34 -s 32768 -P 1 -S 1 -t kernel $DISK 90 sudo cgpt add -b 32802 -s 2000000 -t rootfs $DISK 91 sudo gdisk $DISK # Enter command 'w' to write a protective MBR to the disk 92 93 946. Write U-Boot to the SD card 95 96 sudo dd if=u-boot.kpart of=/dev/sdc1; sync 97 98 997. Start it up 100 101Reboot the device in dev mode. Make sure that you have USB booting enabled. To 102do this, login as root (via Ctrl-Alt-forward_arrow) and type 103'enable_dev_usb_boot'. You only need to do this once. 104 105Reboot the device with the SD card inserted. Press Clrl-U at the developer 106mode screen. It should show something like the following on the display: 107 108 U-Boot 2017.07-00637-g242eb42-dirty (May 22 2017 - 06:14:21 -0600) 109 110 Model: Acer Chromebook 13 CB5-311 111 Board: Google/NVIDIA Nyan-big, ID: 1 112 113 Net: No ethernet found. 114 Hit any key to stop autoboot: 0 115 Tegra124 (Nyan-big) # 116 117 1188. Known problems 119 120On the serial console the word MMC is chopped at the start of the line: 121 122C: sdhci@700b0000: 2, sdhci@700b0400: 1, sdhci@700b0600: 0 123 124This is likely due to some problem with change-over of the serial driver 125during relocation (or perhaps updating the clock setup in board_init()). 126 127 1289. Notes 129 130To check that you copied the u-boot.its file correctly, use these commands. 131You should see that the data at 0x100 in u-boot-chromium.fit is the first few 132bytes of U-Boot: 133 134 hd u-boot-chromium.fit |head -20 135 ... 136 00000100 b8 00 00 ea 14 f0 9f e5 14 f0 9f e5 14 f0 9f e5 |................| 137 138 hd b/nyan-big/u-boot.bin |head 139 00000000 b8 00 00 ea 14 f0 9f e5 14 f0 9f e5 14 f0 9f e5 |................| 140 141 142The 'data' property of the FIT is set up to start at offset 0x100 bytes into 143the file. The change to CONFIG_SYS_TEXT_BASE is also an offset of 0x100 bytes 144from the load address. If this changes, you either need to modify U-Boot to be 145fully relocatable, or expect it to hang. 146 147 148chromebook_jerry 149---------------- 150 151The instruction are similar to those for Nyan with changes as noted below: 152 1531. Patch U-Boot 154 155Open include/configs/rk3288_common.h 156 157Change: 158 159#define CONFIG_SYS_TEXT_BASE 0x00100000 160 161to: 162 163#define CONFIG_SYS_TEXT_BASE 0x02000100 164 165 166 1672. Build U-Boot 168 169 mkdir b 170 make -j8 O=b/chromebook_jerry CROSS_COMPILE=arm-linux-gnueabi- \ 171 chromebook_jerry_defconfig all 172 173 1743. See above 175 1764. Build and sign an image 177 178 ./b/chromebook_jerry/tools/mkimage -f doc/chromium/chromebook_jerry.its \ 179 u-boot-chromium.fit 180 echo test >dummy.txt 181 vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \ 182 --signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \ 183 --version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \ 184 --bootloader dummy.txt --pack u-boot.kpart 185 186 1875. See above 188 1896. See above 190 1917. Start it up 192 193Reboot the device in dev mode. Make sure that you have USB booting enabled. To 194do this, login as root (via Ctrl-Alt-forward_arrow) and type 195'enable_dev_usb_boot'. You only need to do this once. 196 197Reboot the device with the SD card inserted. Press Clrl-U at the developer 198mode screen. It should show something like the following on the display: 199 200 U-Boot 2017.05-00649-g72acdbf-dirty (May 29 2017 - 14:57:05 -0600) 201 202 Model: Google Jerry 203 Net: Net Initialization Skipped 204 No ethernet found. 205 Hit any key to stop autoboot: 0 206 207 2088. Known problems 209 210None as yet. 211 212 2139. Notes 214 215None as yet. 216 217 218Other notes 219=========== 220 221flashrom 222-------- 223 224 Used to make a backup of your firmware, or to replace it. 225 226 See: https://www.chromium.org/chromium-os/packages/cros-flashrom 227 228 229coreboot 230-------- 231 232Coreboot itself is not designed to actually boot an OS. Instead, a program 233called Depthcharge is used. This originally came out of U-Boot and was then 234heavily hacked and modified such that is is almost unrecognisable. It does 235include a very small part of the U-Boot command-line interface but is not 236usable as a general-purpose boot loader. 237 238In addition, it has a very unusual design in that it does not do device init 239itself, but instead relies on coreboot. This is similar to (in U-Boot) having 240a SPI driver with an empty probe() method, relying on whatever was set up 241beforehand. It can be quite hard to figure out between these two code bases 242what settings are actually used. When chain-loading into U-Boot we must be 243careful to reinit anything that U-Boot expects. If not, some peripherals (or 244the whole machine) may not work. This makes the process of chainloading more 245complicated than it could be on some platforms. 246 247Finally, it supports only a subset of the U-Boot's FIT format. In particular 248it uses a fixed address to load the FIT and does not support load/exec 249addresses. This means that U-Boot must be able to boot from whatever 250address Depthcharge happens to use (it is the CONFIG_KERNEL_START setting 251in Depthcharge). In practice this means that the data in the kernel@1 FIT node 252(see above) must start at the same address as U-Boot's CONFIG_SYS_TEXT_BASE. 253