71c255f594
This commit adds supports for building buildroot kernel + rootfs for MT8173 Elm board, also known as Chromebook Elm (https://www.acer.com/ac/en/US/content/series/acerchromebookr13). Though Chrome-OS is officially supproted on this board, the mainline kernel works as well (benchmarks + conformance), and so the 5.9 kernel is used. As the 5.9 kernel isn't yet released, we use the 5.9-rc5 for now, which will be up-revd to 5.9 once its released. Using the mainline kernel means that we have to apply certain patches to get the HDMI screen working. These patches are lying in the "drm-misc-next" list and will make it to the kernel after 5.9. At that time, we will remove the patches and point Buildroot to use the latest kernel (hopefully, 5.10). This commit also adds an ITS file (for creating FIT images), an ARGS file (for providing kernel args) and a "sign.sh" script to generate signed kernel images. Though the "sign.sh" is very similar to the coresponding file under board/chromebook/snow, it cannot be shared between both boards, as the script requires access to the board specific its / args file. Additionally a readme & defconfig is added to help the user get started. Signed-off-by: Bilal Wasim <bilalwasim676@gmail.com> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
57 lines
1.9 KiB
Plaintext
57 lines
1.9 KiB
Plaintext
Mediatek MT8173 aka Chromebook Elm
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==================================
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This file describes booting the Chromebook from an SD card containing
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Buildroot kernel and rootfs, using the original bootloader. This is
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the least invasive way to get Buildroot onto the devices and a good
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starting point.
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The bootloader will only boot a kernel from a GPT partition marked
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bootable with cgpt tool from vboot-utils package.
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The kernel image must be signed using futility from the same package.
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The signing part is done by sign.sh script in this directory.
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It does not really matter where rootfs is as long as the kernel is able
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to find it, but this particular configuration assumes the kernel is on
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partition 1 and rootfs is on partition 2 of the SD card.
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Make sure to check kernel.args if you change this.
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Making the boot media
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---------------------
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Start by configuring and building the images.
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make chromebook_elm_defconfig
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make menuconfig # if necessary
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make
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The important files are:
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uImage.kpart (kernel and device tree, signed)
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rootfs.tar
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bootsd.img (SD card image containing both kernel and rootfs)
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Write the image directly to some SD card.
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WARNING: make sure there is nothing important on that card,
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and double-check the device name!
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SD=/dev/mmcblk1 # may be /dev/sdX on some hosts
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dd if=output/images/bootsd.img of=$SD
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Switching to developer mode and booting from SD
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-----------------------------------------------
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Power Chromebook down, then power it up while holding Esc+F3.
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BEWARE: switching to developer mode deletes all user data.
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Create backups if you need them.
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While in developer mode, Chromebook will boot into a white screen saying
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"OS verification is off".
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Press Ctrl-D at this screen to boot Chromium OS from eMMC.
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Press Ctrl-U at this screen to boot from SD (or USB)
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Press Power to power it off.
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Do NOT press Space unless you mean it.
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This will switch it back to normal mode.
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The is no way to get rid of the white screen without re-flashing the bootloader.
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