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.. SPDX-License-Identifier: GPL-2.0+
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.. Copyright 2020 Google LLC
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Chromium OS Support in U-Boot
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=============================
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Introduction
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------------
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This describes how to use U-Boot with Chromium OS. Several options are
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available:
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- Running U-Boot from the 'altfw' feature, which is available on selected
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Chromebooks from 2019 onwards (initially Grunt). Press '1' from the
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developer-mode screen to get into U-Boot. See here for details:
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https://chromium.googlesource.com/chromiumos/docs/+/HEAD/developer_mode.md
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- Running U-Boot from the disk partition. This involves signing U-Boot and
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placing it on the disk, for booting as a 'kernel'. See
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:doc:`chainload` for information on this. This is the only
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option on non-U-Boot Chromebooks from 2013 to 2018 and is somewhat
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more involved.
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- Running U-Boot with Chromium OS verified boot. This allows U-Boot to be
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used instead of either or both of depthcharge (a bootloader which forked
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from U-Boot in 2013) and coreboot. See :doc:`run_vboot` for more
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information on this.
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- Running U-Boot from coreboot. This allows U-Boot to run on more devices
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since many of them only support coreboot as the bootloader and have
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no bare-metal support in U-Boot. For this, use the 'coreboot' target.
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- Running U-Boot and booting into a Chrome OS image, but without verified
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boot. This can be useful for testing.
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Talks and documents
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-------------------
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Here is some material relevant to Chromium OS verified boot with U-Boot:
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- "U-Boot with Chrome OS and firmware packaging"
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- Author: Simon Glass
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- Presented at Open Source Firmware Conference 2018, Erlangen
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- Describes the work in progress as at the end of 2018
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- Slides at `OSFC <https://2018.osfc.io/uploads/talk/paper/26/U-Boot_with_Chrome_OS_and_firmware_packaging.pdf>`_
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- `Youtube video 'OSFC - U-Boot with Chrome OS and firmware packaging' <https://www.youtube.com/watch?v=1jknxUvmwpo>`_
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- "Verified Boot in Chrome OS and how to make it work for you"
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- Author: Simon Glass
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- Presented at ELCE 2013, Edinburgh
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- Describes the original 2013 implementation as shipped on snow (first
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`ARM Chromebook was a Samsung Chromebook <https://www.cnet.com/products/samsung-series-3-chromebook-xe303c12-11-6-exynos-5250-2-gb-ram-16-gb-ssd-bilingual-english-french/>`_
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with Samsung Exynos5250 `review <https://www.cnet.com/reviews/samsung-chromebook-series-3-review/>`_),
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spring (`HP Chromebook 11 <https://www.cnet.com/products/hp-chromebook-11-g2-11-6-exynos-5250-4-gb-ram-16-gb-emmc/>`_)
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and pit/pi (`Samsung Chromebook 2 <https://www.cnet.com/products/samsung-chromebook-2-xe503c12-11-6-exynos-5-octa-4-gb-ram-16-gb-ssd/>`_
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with Exynos 5 Octa 5420 in 2014).
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- Slides at `Google research <https://research.google/pubs/pub42038/>`_
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- `Youtube video 'Verified Boot on Chrome OS and How to do it yourself' <https://www.youtube.com/watch?v=kdpZC9jFzZA>`_
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- "Chrome University 2018: Chrome OS Firmware and Verified Boot 201"
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- Author: Duncan Laurie
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- Describes Chrome OS firmware as of 2018 and includes a wide range of
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topics. This has no U-Boot information, but does cover coreboot and also
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talks about the Chrome OS EC and Security chip. This is probably the
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best introduction talk.
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- `Youtube video 'Chrome University 2018: Chrome OS Firmware and Verified Boot 201' <https://www.youtube.com/watch?v=WY2sWpuda2g>`_
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- `Chromium OS U-Boot <https://www.chromium.org/developers/u-boot>`_
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- `Firmware porting Guide <https://www.chromium.org/chromium-os/firmware-porting-guide>`_
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