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The U-Boot "stemmy" board is mainly intended to simplify booting mainline Linux on various smartphones from Samsung based on ST-Ericsson Ux500. While the mainline kernel is working great, there are still some features missing there. In particular, it is currently not possible to charge the battery when using the mainline kernel. This means that it is still necessary to boot the downstream/vendor kernel from Samsung sometimes to charge the device. That kernel is ancient, still uses board files + ATAGS instead of device trees and relies on a strange very long kernel command line hardcoded in the Samsung bootloader. Actually, since mainline is booted with device trees there is a very simple way to make the old downstream kernel work as well: We can simply take most of the ATAGS passed to U-Boot from the Samsung bootloader and copy them as-is when booting a kernel without device tree. That way the long command line and other needed ATAGS are copied as-is without having to bother with them. The only exception is the ATAG_INITRD - since the initrd is loaded by U-Boot, the atag for that should be generated in U-Boot so it points to the correct address. All other ATAGS are copied as-is and not generated in U-Boot. Also use the chance and provide a serial# for U-Boot by parsing the ATAG_SERIAL that is also passed by the Samsung bootloader. Signed-off-by: Stephan Gerhold <stephan@gerhold.net> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> |
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ST-Ericsson U8500 Samsung "stemmy" board
========================================
The "stemmy" board supports Samsung smartphones released with
the ST-Ericsson NovaThor U8500 SoC, e.g.
- Samsung Galaxy S III mini (GT-I8190) "golden"
- Samsung Galaxy S Advance (GT-I9070) "janice"
- Samsung Galaxy Xcover 2 (GT-S7710) "skomer"
- Samsung Galaxy Ace 2 (GT-I8160) "codina"
and likely others as well (untested).
At the moment, U-Boot is intended to be chain-loaded from
the original Samsung bootloader, not replacing it entirely.
Installation
------------
1. Setup cross compiler, e.g. export CROSS_COMPILE=arm-none-eabi-
2. make stemmy_defconfig
3. make
For newer devices (golden and skomer), the U-Boot binary has to be packed into
an Android boot image. janice boots the raw U-Boot binary from the boot partition.
4. Obtain mkbootimg, e.g. https://android.googlesource.com/platform/system/core/+/refs/tags/android-7.1.2_r37/mkbootimg/mkbootimg
5. mkbootimg \
--kernel=u-boot.bin \
--base=0x00000000 \
--kernel_offset=0x00100000 \
--ramdisk_offset=0x02000000 \
--tags_offset=0x00000100 \
--output=u-boot.img
6. Enter Samsung download mode (press Power + Home + Volume Down)
7. Flash U-Boot image to Android boot partition using Heimdall:
https://gitlab.com/BenjaminDobell/Heimdall
heimdall flash --Kernel u-boot.(bin|img)
8. After reboot U-Boot prompt should appear via UART.
UART
----
UART is available through the micro USB port, similar to the Carkit standard.
With a ~619kOhm resistor between ID and GND, 1.8V RX/TX is available at D+/D-.
Make sure to connect the UART cable *before* turning on the phone.