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https://github.com/AsahiLinux/u-boot
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U-boot is intended to replace linux kernel in android boot image(ABL), and it's FIT payload to replace initramfs file. The boot process is similar to boot image with linux: - android bootloader (ABL) unpacks android boot image - ABL sets `linux,initrd-start property` in chosen node in unpacked FDT - ABL sets x0 register to FDT address, and passes control to u-boot - u-boot reads x0 register, and stores it in `prevbl_fdt_addr` env variable - u-boot reads `linux,initrd-start` property, and stores it in `prevbl_initrd_start_addr` In this way, u-boot bootcmd relies on `prevbl_initrd_start_addr` env variable, and boils down to `bootm $prevbl_initrd_start_addr`. If more control on boot process is desired, pack a boot script in FIT image, and put it to default configuration What done: - Rearrange defconfig option order - Add CONFIG_SAVE_PREV_BL_* options - Doc updates: - remove wrong SBOOT memory corruption note, because memory is changed during u-boot bringup process, not by SBOOT - put payload on ramdisk place in abl boot image creation step Signed-off-by: Dzmitry Sankouski <dsankouski@gmail.com>
85 lines
2.2 KiB
ReStructuredText
85 lines
2.2 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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.. sectionauthor:: Dzmitry Sankouski <dsankouski@gmail.com>
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Samsung 2017 A series phones
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============================
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About this
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----------
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This document describes the information about Samsung A(7/5/3) 2017 midrange
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phones and u-boot usage steps.
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U-Boot can be used as a chain-loaded bootloader to replace Samsung's original SBOOT bootloader.
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It is loaded as an Android boot image through SBOOT.
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Phone specs
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-----------
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A3 (SM-A320) (a3y17lte)
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^^^^^^^^^^^^^^^^^^^^^^^
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- 4.7 AMOLED display
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- Exynos 7870 SoC
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- 16GB flash
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- 2GB RAM
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.. A3 2017 wiki page: https://en.wikipedia.org/wiki/Samsung_Galaxy_A3_(2017)
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A5 (SM-A520) (a5y17lte)
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^^^^^^^^^^^^^^^^^^^^^^^
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- 5.2 AMOLED display
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- Exynos 7880 SoC
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- 32GB flash
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- 3GB RAM
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.. A5 2017 wiki page: https://en.wikipedia.org/wiki/Samsung_Galaxy_A5_(2017)
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A7 (SM-A720) (a5y17lte)
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^^^^^^^^^^^^^^^^^^^^^^^
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- 5.7 AMOLED display
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- Exynos 7880 SoC
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- 32GB flash
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- 3GB RAM
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.. A7 2017 wiki page: https://en.wikipedia.org/wiki/Samsung_Galaxy_A7_(2017)
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Installation
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------------
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Building u-boot
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^^^^^^^^^^^^^^^
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First, setup ``CROSS_COMPILE`` for aarch64.
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Then, build U-Boot for your phone, for example ``a5y17lte``::
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$ export CROSS_COMPILE=<aarch64 toolchain prefix>
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$ make a5y17lte_defconfig
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$ make
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This will build ``u-boot.bin`` in the configured output directory.
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Payload
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^^^^^^^
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What is a payload?
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""""""""""""""""""
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A payload file is a file to be used instead of linux kernel in android boot image.
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This file will be loaded into memory, and executed by SBOOT,
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and is therefore SBOOT's payload.
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It may be pure u-boot (with loading u-boot's payload from flash in mind),
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or u-boot + u-boot's payload.
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Creating payload file
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"""""""""""""""""""""
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- Assemble FIT image for your kernel
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Creating android boot image
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"""""""""""""""""""""""""""
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Once payload created, it's time for android image::
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uboot=<path to u-boot.bin file>
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ramdisk=<path to FIT payload file>
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mkbootimg --base 0x40000000 --kernel_offset 0x00000000 --ramdisk_offset 0x01000000 --tags_offset 0x00000100 --pagesize 2048 --second_offset 0x00f00000 --kernel "$uboot" --ramdisk "$ramdisk" -o uboot.img
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Note, that stock Samsung bootloader ignores offsets, set in mkbootimg.
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Flashing
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""""""""
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Flash like regular android boot image.
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