doc/README.chromium

   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. Patch U-Boot
  47
  48 Open include/configs/tegra124-common.h
  49
  50 Change:
  51
  52 #define CONFIG_SYS_TEXT_BASE    0x80110000
  53
  54 to:
  55
  56 #define CONFIG_SYS_TEXT_BASE    0x81000100
  57
  58
  59 2. 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
  65 3. Select a .its file
  66
  67 Select something from doc/chromium which matches your board, or create your
  68 own.
  69
  70 Note that the device tree node is required, even though it is not actually
  71 used by U-Boot. This is because the Chromebook expects to pass it to the
  72 kernel, and crashes if it is not present.
  73
  74
  75 4. 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
  85 5. 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
  94 6. Write U-Boot to the SD card
  95
  96    sudo dd if=u-boot.kpart of=/dev/sdc1; sync
  97
  98
  99 7. Start it up
 100
 101 Reboot the device in dev mode. Make sure that you have USB booting enabled. To
 102 do this, login as root (via Ctrl-Alt-forward_arrow) and type
 103 'enable_dev_usb_boot'. You only need to do this once.
 104
 105 Reboot the device with the SD card inserted. Press Clrl-U at the developer
 106 mode 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
 118 8. Known problems
 119
 120 On the serial console the word MMC is chopped at the start of the line:
 121
 122 C:   sdhci@700b0000: 2, sdhci@700b0400: 1, sdhci@700b0600: 0
 123
 124 This is likely due to some problem with change-over of the serial driver
 125 during relocation (or perhaps updating the clock setup in board_init()).
 126
 127
 128 9. Notes
 129
 130 To check that you copied the u-boot.its file correctly, use these commands.
 131 You should see that the data at 0x100 in u-boot-chromium.fit is the first few
 132 bytes 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
 142 The 'data' property of the FIT is set up to start at offset 0x100 bytes into
 143 the file. The change to CONFIG_SYS_TEXT_BASE is also an offset of 0x100 bytes
 144 from the load address. If this changes, you either need to modify U-Boot to be
 145 fully relocatable, or expect it to hang.
 146
 147
 148 chromebook_jerry
 149 ----------------
 150
 151 The instruction are similar to those for Nyan with changes as noted below:
 152
 153 1. Patch U-Boot
 154
 155 Open include/configs/rk3288_common.h
 156
 157 Change:
 158
 159 #define CONFIG_SYS_TEXT_BASE            0x00100000
 160
 161 to:
 162
 163 #define CONFIG_SYS_TEXT_BASE            0x02000100
 164
 165
 166
 167 2. 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
 174 3. See above
 175
 176 4. 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
 187 5. See above
 188
 189 6. See above
 190
 191 7. Start it up
 192
 193 Reboot the device in dev mode. Make sure that you have USB booting enabled. To
 194 do this, login as root (via Ctrl-Alt-forward_arrow) and type
 195 'enable_dev_usb_boot'. You only need to do this once.
 196
 197 Reboot the device with the SD card inserted. Press Clrl-U at the developer
 198 mode 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
 208 8. Known problems
 209
 210 None as yet.
 211
 212
 213 9. Notes
 214
 215 None as yet.
 216
 217
 218 Other notes
 219 ===========
 220
 221 flashrom
 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
 229 coreboot
 230 --------
 231
 232 Coreboot itself is not designed to actually boot an OS. Instead, a program
 233 called Depthcharge is used. This originally came out of U-Boot and was then
 234 heavily hacked and modified such that is is almost unrecognisable. It does
 235 include a very small part of the U-Boot command-line interface but is not
 236 usable as a general-purpose boot loader.
 237
 238 In addition, it has a very unusual design in that it does not do device init
 239 itself, but instead relies on coreboot. This is similar to (in U-Boot) having
 240 a SPI driver with an empty probe() method, relying on whatever was set up
 241 beforehand. It can be quite hard to figure out between these two code bases
 242 what settings are actually used. When chain-loading into U-Boot we must be
 243 careful to reinit anything that U-Boot expects. If not, some peripherals (or
 244 the whole machine) may not work. This makes the process of chainloading more
 245 complicated than it could be on some platforms.
 246
 247 Finally, it supports only a subset of the U-Boot's FIT format. In particular
 248 it uses a fixed address to load the FIT and does not support load/exec
 249 addresses. This means that U-Boot must be able to boot from whatever
 250 address Depthcharge happens to use (it is the CONFIG_KERNEL_START setting
 251 in 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.