1 Running U-Boot from coreboot on Chromebooks 2 =========================================== 3 4 U-Boot can be used as a secondary boot loader in a few situations such as from 5 UEFI and coreboot (see README.x86). Recent Chromebooks use coreboot even on 6 ARM platforms to start up the machine. 7 8 This document aims to provide a guide to booting U-Boot on a Chromebook. It 9 is only a starting point, and there are many guides on the interwebs. But 10 placing this information in the U-Boot tree should make it easier to find for 11 those who use U-Boot habitually. 12 13 Most of these platforms are supported by U-Boot natively, but it is risky to 14 replace the ROM unless you have a servo board and cable to restore it with. 15 16 17 For all of these the standard U-Boot build instructions apply. For example on 18 ARM: 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 24 You can obtain the vbutil_kernel utility here: 25 26 https://drive.google.com/open?id=0B7WYZbZ9zd-3dHlVVXo4VXE2T0U 27 28 29 Snow (Samsung ARM Chromebook) 30 ----------------------------- 31 32 See here: 33 34 https://www.chromium.org/chromium-os/firmware-porting-guide/using-nv-u-boot-on-the-samsung-arm-chromebook 35 36 37 Nyan-big 38 -------- 39 40 Compiled based on information here: 41 https://lists.denx.de/pipermail/u-boot/2015-March/209530.html 42 https://git.collabora.com/cgit/user/tomeu/u-boot.git/commit/?h=nyan-big 43 https://lists.denx.de/pipermail/u-boot/2017-May/289491.html 44 https://github.com/chromeos-nvidia-androidtv/gnu-linux-on-acer-chromebook-13#copy-data-to-the-sd-card 45 46 1. Build U-Boot 47 48 mkdir b 49 make -j8 O=b/nyan-big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all 50 51 52 2. Select a .its file 53 54 Select something from doc/chromium which matches your board, or create your 55 own. 56 57 Note that the device tree node is required, even though it is not actually 58 used by U-Boot. This is because the Chromebook expects to pass it to the 59 kernel, and crashes if it is not present. 60 61 62 3. Build and sign an image 63 64 ./b/nyan-big/tools/mkimage -f doc/chromium/nyan-big.its u-boot-chromium.fit 65 echo test >dummy.txt 66 vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \ 67 --signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \ 68 --version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \ 69 --bootloader dummy.txt --pack u-boot.kpart 70 71 72 4. Prepare an SD card 73 74 DISK=/dev/sdc # Replace with your actual SD card device 75 sudo cgpt create $DISK 76 sudo cgpt add -b 34 -s 32768 -P 1 -S 1 -t kernel $DISK 77 sudo cgpt add -b 32802 -s 2000000 -t rootfs $DISK 78 sudo gdisk $DISK # Enter command 'w' to write a protective MBR to the disk 79 80 81 5. Write U-Boot to the SD card 82 83 sudo dd if=u-boot.kpart of=/dev/sdc1; sync 84 85 86 6. Start it up 87 88 Reboot the device in dev mode. Make sure that you have USB booting enabled. To 89 do this, login as root (via Ctrl-Alt-forward_arrow) and type 90 'enable_dev_usb_boot'. You only need to do this once. 91 92 Reboot the device with the SD card inserted. Press Clrl-U at the developer 93 mode screen. It should show something like the following on the display: 94 95 U-Boot 2017.07-00637-g242eb42-dirty (May 22 2017 - 06:14:21 -0600) 96 97 Model: Acer Chromebook 13 CB5-311 98 Board: Google/NVIDIA Nyan-big, ID: 1 99 100 Net: No ethernet found. 101 Hit any key to stop autoboot: 0 102 Tegra124 (Nyan-big) # 103 104 105 7. Known problems 106 107 On the serial console the word MMC is chopped at the start of the line: 108 109 C: sdhci@700b0000: 2, sdhci@700b0400: 1, sdhci@700b0600: 0 110 111 This is likely due to some problem with change-over of the serial driver 112 during relocation (or perhaps updating the clock setup in board_init()). 113 114 115 9. Notes 116 117 To check that you copied the u-boot.its file correctly, use these commands. 118 You should see that the data at 0x100 in u-boot-chromium.fit is the first few 119 bytes of U-Boot: 120 121 hd u-boot-chromium.fit |head -20 122 ... 123 00000100 b8 00 00 ea 14 f0 9f e5 14 f0 9f e5 14 f0 9f e5 |................| 124 125 hd b/nyan-big/u-boot.bin |head 126 00000000 b8 00 00 ea 14 f0 9f e5 14 f0 9f e5 14 f0 9f e5 |................| 127 128 129 The 'data' property of the FIT is set up to start at offset 0x100 bytes into 130 the file. The change to CONFIG_SYS_TEXT_BASE is also an offset of 0x100 bytes 131 from the load address. If this changes, you either need to modify U-Boot to be 132 fully relocatable, or expect it to hang. 133 134 135 chromebook_jerry 136 ---------------- 137 138 The instruction are similar to those for Nyan with changes as noted below: 139 140 1. Patch U-Boot 141 142 Open include/configs/rk3288_common.h 143 144 Change: 145 146 #define CONFIG_SYS_TEXT_BASE 0x00100000 147 148 to: 149 150 #define CONFIG_SYS_TEXT_BASE 0x02000100 151 152 153 154 2. Build U-Boot 155 156 mkdir b 157 make -j8 O=b/chromebook_jerry CROSS_COMPILE=arm-linux-gnueabi- \ 158 chromebook_jerry_defconfig all 159 160 161 3. See above 162 163 4. Build and sign an image 164 165 ./b/chromebook_jerry/tools/mkimage -f doc/chromium/chromebook_jerry.its \ 166 u-boot-chromium.fit 167 echo test >dummy.txt 168 vbutil_kernel --arch arm --keyblock doc/chromium/devkeys/kernel.keyblock \ 169 --signprivate doc/chromium/devkeys/kernel_data_key.vbprivk \ 170 --version 1 --config dummy.txt --vmlinuz u-boot-chromium.fit \ 171 --bootloader dummy.txt --pack u-boot.kpart 172 173 174 5. See above 175 176 6. See above 177 178 7. Start it up 179 180 Reboot the device in dev mode. Make sure that you have USB booting enabled. To 181 do this, login as root (via Ctrl-Alt-forward_arrow) and type 182 'enable_dev_usb_boot'. You only need to do this once. 183 184 Reboot the device with the SD card inserted. Press Clrl-U at the developer 185 mode screen. It should show something like the following on the display: 186 187 U-Boot 2017.05-00649-g72acdbf-dirty (May 29 2017 - 14:57:05 -0600) 188 189 Model: Google Jerry 190 Net: Net Initialization Skipped 191 No ethernet found. 192 Hit any key to stop autoboot: 0 193 194 195 8. Known problems 196 197 None as yet. 198 199 200 9. Notes 201 202 None as yet. 203 204 205 Other notes 206 =========== 207 208 flashrom 209 -------- 210 211 Used to make a backup of your firmware, or to replace it. 212 213 See: https://www.chromium.org/chromium-os/packages/cros-flashrom 214 215 216 coreboot 217 -------- 218 219 Coreboot itself is not designed to actually boot an OS. Instead, a program 220 called Depthcharge is used. This originally came out of U-Boot and was then 221 heavily hacked and modified such that is is almost unrecognisable. It does 222 include a very small part of the U-Boot command-line interface but is not 223 usable as a general-purpose boot loader. 224 225 In addition, it has a very unusual design in that it does not do device init 226 itself, but instead relies on coreboot. This is similar to (in U-Boot) having 227 a SPI driver with an empty probe() method, relying on whatever was set up 228 beforehand. It can be quite hard to figure out between these two code bases 229 what settings are actually used. When chain-loading into U-Boot we must be 230 careful to reinit anything that U-Boot expects. If not, some peripherals (or 231 the whole machine) may not work. This makes the process of chainloading more 232 complicated than it could be on some platforms. 233 234 Finally, it supports only a subset of the U-Boot's FIT format. In particular 235 it uses a fixed address to load the FIT and does not support load/exec 236 addresses. This means that U-Boot must be able to boot from whatever 237 address Depthcharge happens to use (it is the CONFIG_KERNEL_START setting 238 in Depthcharge). In practice this means that the data in the kernel@1 FIT node 239 (see above) must start at the same address as U-Boot's CONFIG_SYS_TEXT_BASE. 240
