u-boot-brain

History

Stephan Gerhold 43d28855d8 board: Add new Samsung "stemmy" board based on ST-Ericsson U8500 The ST-Ericsson U8500 SoC has been used in mass-production for some Android smartphones released around 2012. In particular, Samsung has released more than 5 different smartphones based on U8500, e.g. - Samsung Galaxy S III mini (GT-I8190) "golden" - Samsung Galaxy S Advance (GT-I9070) "janice" - Samsung Galaxy Xcover 2 (GT-S7710) "skomer" and a few others. Mainline Linux has great support for the Ux500 SoC, so these smartphones can also run Linux mainline quite well. Unfortunately, the original Samsung bootloader used on these devices has limitations that prevent booting Linux mainline directly. It keeps the L2 cache enabled, which causes Linux to crash very early, shortly after decompressing the kernel. Using U-Boot allows to circumvent these limitations. We can let the Samsung bootloader chain-load U-Boot and U-Boot locks the L2 cache before booting into Linux. U-Boot has several other advantages - it supports device-trees directly and we are no longer limited to flashing Android boot images through Samsung's proprietary download mode. The Samsung "stemmy" board covers all Samsung devices based on U8500. Add minimal support for "stemmy". For now only UART is supported but this will be extended later. Signed-off-by: Stephan Gerhold <stephan@gerhold.net> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>		2020-01-22 17:47:57 -05:00
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Kconfig	board: Add new Samsung "stemmy" board based on ST-Ericsson U8500	2020-01-22 17:47:57 -05:00
MAINTAINERS	board: Add new Samsung "stemmy" board based on ST-Ericsson U8500	2020-01-22 17:47:57 -05:00
Makefile	board: Add new Samsung "stemmy" board based on ST-Ericsson U8500	2020-01-22 17:47:57 -05:00
README	board: Add new Samsung "stemmy" board based on ST-Ericsson U8500	2020-01-22 17:47:57 -05:00
stemmy.c	board: Add new Samsung "stemmy" board based on ST-Ericsson U8500	2020-01-22 17:47:57 -05:00

README

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"

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.