Chromium OS Support in U-Boot¶
This describes how to use U-Boot with Chromium OS. Several options are available:
- Running U-Boot from the ‘altfw’ feature, which is available on selected Chromebooks from 2019 onwards (initially Grunt). Press ‘1’ from the developer-mode screen to get into U-Boot. See here for details: https://chromium.googlesource.com/chromiumos/docs/+/HEAD/developer_mode.md
- Running U-Boot from the disk partition. This involves signing U-Boot and placing it on the disk, for booting as a ‘kernel’. See Running U-Boot from coreboot on Chromebooks for information on this. This is the only option on non-U-Boot Chromebooks from 2013 to 2018 and is somewhat more involved.
- Running U-Boot with Chromium OS verified boot. This allows U-Boot to be used instead of either or both of depthcharge (a bootloader which forked from U-Boot in 2013) and coreboot. See Running U-Boot with Chromium OS verified boot for more information on this.
- Running U-Boot from coreboot. This allows U-Boot to run on more devices since many of them only support coreboot as the bootloader and have no bare-metal support in U-Boot. For this, use the ‘coreboot’ target.
- Running U-Boot and booting into a Chrome OS image, but without verified boot. This can be useful for testing.
Talks and documents¶
Here is some material relevant to Chromium OS verified boot with U-Boot:
- “U-Boot with Chrome OS and firmware packaging”
- Author: Simon Glass
- Presented at Open Source Firmware Conference 2018, Erlangen
- Describes the work in progress as at the end of 2018
- Slides at OSFC
- Youtube video ‘OSFC - U-Boot with Chrome OS and firmware packaging’
- “Verified Boot in Chrome OS and how to make it work for you”
- Author: Simon Glass
- Presented at ELCE 2013, Edinburgh
- Describes the original 2013 implementation as shipped on snow (first ARM Chromebook was a Samsung Chromebook with Samsung Exynos5250 review), spring (HP Chromebook 11) and pit/pi (Samsung Chromebook 2 with Exynos 5 Octa 5420 in 2014).
- Slides at Google research
- Youtube video ‘Verified Boot on Chrome OS and How to do it yourself’
- “Chrome University 2018: Chrome OS Firmware and Verified Boot 201”
- Author: Duncan Laurie
- Describes Chrome OS firmware as of 2018 and includes a wide range of topics. This has no U-Boot information, but does cover coreboot and also talks about the Chrome OS EC and Security chip. This is probably the best introduction talk.
- Youtube video ‘Chrome University 2018: Chrome OS Firmware and Verified Boot 201’
- Chromium OS U-Boot
- Firmware porting Guide