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| -rw-r--r-- | doc/chromium/devkeys/kernel_data_key.vbprivk | bin | 0 -> 1199 bytes |
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diff --git a/doc/README.chromium b/doc/README.chromium new file mode 100644 index 00000000000..61e285da5ea --- /dev/null +++ b/doc/README.chromium @@ -0,0 +1,182 @@ +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. Patch U-Boot + +Open include/configs/tegra124-common.h + +Change: + +#define CONFIG_SYS_TEXT_BASE 0x80110000 + +to: + +#define CONFIG_SYS_TEXT_BASE 0x81000100 + + +2. Build U-Boot + + mkdir b + make -j8 O=b/nyan-big CROSS_COMPILE=arm-linux-gnueabi- nyan-big_defconfig all + + +3. 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. + + +4. 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 + + +5. 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 + + +6. Write U-Boot to the SD card + + sudo dd if=u-boot.kpart of=/dev/sdc1; sync + + +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 2017.07-00637-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) # + + +8. 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. + + +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. diff --git a/doc/chromium/devkeys/kernel.keyblock b/doc/chromium/devkeys/kernel.keyblock Binary files differnew file mode 100644 index 00000000000..9740be4e600 --- /dev/null +++ b/doc/chromium/devkeys/kernel.keyblock diff --git a/doc/chromium/devkeys/kernel_data_key.vbprivk b/doc/chromium/devkeys/kernel_data_key.vbprivk Binary files differnew file mode 100644 index 00000000000..8d392fb294c --- /dev/null +++ b/doc/chromium/devkeys/kernel_data_key.vbprivk |