Samsung Galaxy S9 (samsung-starqltechn)/u-boot

U-boot can be used as a second stage bootloader, and also a tool to experiment with uart on usb.
Using u-boot as a second stage bootloader involves packing u-boot instead of linux kernel, and u-boot's payload instead of initramfs in android boot image.
=== Second stage bootloader ===
In this section, we'll generate an android boot image with u-boot as second stage bootloader for linux kernel in FIT image format.
==== Build u-boot ====
* clone u-boot repo
* prepare default config export CROSS_COMPILE=aarch64-linux-gnu- && make starqltechn_defconfig && make
* build make
* create payload for SBOOT by gzipping and appending dtb: 
gzip -k u-boot.bin
cat u-boot.bin.gz u-boot.dtb > u-boot.gz-dtb
==== Build kernel ====
* build starqltechn kernel with envkernel.sh
==== Generate android boot image ====
* create bootscript.sh file: bootm $prevbl_initrd_start_addr
* build ramdisk
* create boot.its file, describing u-boot's payload:
 
/dts-v1/;
/ {
 description = "Samsung S9 SM-G9600 starqltechn FIT Image";
 #address-cells = <1>;
 images {
 bootscript {
 description = "Boot script";
 data = /incbin/("bootscript.sh");
 type = "script";
 compression = "none";
 load = <0x90000000>;
 entry = <0x90000000>;
 hash {
 algo = "sha1";
 };
 };
 kernel {
 description = "Kernel";
 //data = /incbin/("Image.gz");
 data = /incbin/(".output/arch/arm64/boot/Image.gz");
 type = "kernel";
 arch = "arm64";
 os = "linux";
 compression = "gzip";
 load = <0x80000000>;
 entry = <0x80000000>;
 hash {
 algo = "sha1";
 };
 };
 fdt {
 description = "DTB";
 data = /incbin/(".output/arch/arm64/boot/dts/qcom/sdm845-samsung-starqltechn.dtb");
 type = "flat_dt";
 arch = "arm64";
 compression = "none";
 load = <0x82a80000>;
 entry = <0x82a80000>;
 hash {
 algo = "sha1";
 };
 };
 initrd {
 description = "Initrd";
 data = /incbin/("<ramdisk path>");
 type = "ramdisk";
 arch = "arm64";
 os = "linux";
 compression = "none";
 hash {
 algo = "sha1";
 };
 };
 };
 configurations {
 default = "standard";
 standard {
 description = "Standard Boot";
 kernel = "kernel";
 fdt = "fdt";
 ramdisk = "initrd";
 hash {
 algo = "sha1";
 };
 };
 };
};
* build u-boot payload mkimage -f boot.its boot.itb
* make android boot image:
mkbootimg --base 0x0 --kernel_offset 0x00008000 --ramdisk_offset 0x02000000 --tags_offset 0x01e00000 --pagesize 4096 --second_offset 0x00f00000 \
--ramdisk boot.itb \
--kernel u-boot.gz-dtb -o boot.img
==== Running ====
* flash android boot image.
* Reboot to system, give it some time to boot
* Read logs. See Getting logs from pstore''
==== Development ====
See also Initramfs_development
=== Booting android with u-boot ===
==== Assemble FIT image from android boot image ====
* Build u-boot with config:
CONFIG_ARM=y
CONFIG_SKIP_LOWLEVEL_INIT=y
CONFIG_COUNTER_FREQUENCY=19000000
CONFIG_POSITION_INDEPENDENT=y
CONFIG_ARCH_SNAPDRAGON=y
CONFIG_DEFAULT_DEVICE_TREE="starqltechn"
CONFIG_TARGET_STARQLTECHN=y
CONFIG_IDENT_STRING="\nSamsung S9 SM-G9600"
CONFIG_SYS_LOAD_ADDR=0x80000000
CONFIG_FIT=y
CONFIG_FIT_VERBOSE=y
CONFIG_BOOTDELAY=5
CONFIG_USE_PREBOOT=y
CONFIG_SAVE_PREV_BL_FDT_ADDR=y
CONFIG_SAVE_PREV_BL_INITRAMFS_START_ADDR=y
# CONFIG_DISPLAY_CPUINFO is not set
CONFIG_HUSH_PARSER=y
CONFIG_SYS_MAXARGS=64
CONFIG_SYS_CBSIZE=512
CONFIG_SYS_PBSIZE=532
CONFIG_CMD_GPIO=y
CONFIG_CMD_BMP=y
# CONFIG_NET is not set
# CONFIG_DM_STDIO is not set
CONFIG_CLK=y
CONFIG_MSM_GPIO=y
CONFIG_PM8916_GPIO=y
CONFIG_PINCTRL=y
CONFIG_DM_PMIC=y
CONFIG_PMIC_PM8916=y
CONFIG_REQUIRE_SERIAL_CONSOLE=y
CONFIG_MSM_GENI_SERIAL=y
CONFIG_MMC_SDHCI=y
CONFIG_MMC_SDHCI_MSM=y
CONFIG_CMD_MMC=y
CONFIG_SPMI_MSM=y
CONFIG_FS_FAT=y
CONFIG_DM_VIDEO=y
CONFIG_SYS_WHITE_ON_BLACK=y
CONFIG_VIDEO_SIMPLE=y
CONFIG_LMB_MAX_REGIONS=64
CONFIG_BAUDRATE=921600
* Disassemble android image(use android kitchen)
* Split kernel and dtb image; disassemble dtb image into separate files
* Find correct dtb file(check msm-id and board id properties on running android)
* Copy kernel commandline from running android
* Create a bootscript.sh (it searches kaslr address and adjusts kernel load address):
echo "##############################################"
echo "##############################################"
echo "searching for sboot load address..."
addr=0x80000038
addr2=0x80000050
setenv arm64 0x644d5241
until itest *$addr == 0x644d5241 && itest *$addr2 == 0x6d3a8; do
 setexpr addr $addr + 0x1000
 setexpr addr2 $addr2 + 0x1000
done
setexpr addr $addr - 0x38
echo "sboot loaded payload at 0x$addr"
setenv bootm_low "0x$addr"
setenv bootm_size 0x5000000
fdt addr $prevbl_initrd_start_addr
fdt set "/images/kernel" "load" "<0x$addr>"
fdt set "/images/kernel" "entry" "<0x$addr>"
fdt addr $prevbl_fdt_addr
fdt print "/chosen"
bootm $image_address#standard $image_address#standard $prevbl_fdt_addr
* Create a fit image source file using kernel, and ramdisk from android and boot:
/dts-v1/;
/ {
 description = "Samsung S9 SM-G9600 starqltechn FIT Image";
 #address-cells = <1>;
 images {
 prebootscript {
 description = "pre Boot script";
 data = /incbin/("bootscript.sh");
 type = "script";
 compression = "none";
 load = <0x83000000>;
 entry = <0x83000000>;
 hash {
 algo = "sha1";
 };
 };
 kernel {
 description = "Kernel";
 data = /incbin/("split_img/kernel");
 type = "kernel";
 arch = "arm64";
 os = "linux";
 compression = "gzip";
 load = <0x80200000>;
 entry = <0x80200000>;
 hash {
 algo = "sha1";
 };
 };
 initrd {
 description = "Initrd";
 compression = "none";
 data = /incbin/("split_img/boot.img-ramdisk.cpio.gz");
 type = "ramdisk";
 arch = "arm64";
 os = "linux";
 hash {
 algo = "sha1";
 };
 };
 };
 configurations {
 default = "standard";
 standard {
 description = "Standard Boot";
 kernel = "kernel";
 ramdisk = "initrd";
 hash {
 algo = "sha1";
 };
 };
 };
}; 
* assemble boot image:
gzip -c u-boot.bin > u-boot.bin.gz
mkimage -f boot_image.dts boot.itb
cat u-boot.bin.gz split_img/dtbdump_15.dtb > u-boot.gz-dtb
mkbootimg --base 0x0 --kernel_offset 0x00008000 --ramdisk_offset 0x02000000 --tags_offset 0x01e00000 --pagesize 4096 --second_offset 0x00f00000 \
--kernel u-boot.gz-dtb \
--ramdisk boot.itb \
-o boot.img
==== Android quirks ====
* boot image should be reassembled from android boot image (because it contains os version and patch level). Failure to provide version and patch level leads to qseecom encryption key update failure.
* linux kernel should be loaded at stock bootloader kaslr address. qseecom trusted app reads memory map from physical address, so if kernel loaded at arbitrary address, it fails
=== Experimenting: procedure with usb-uart cable ===
This intendent for getting uart console at u-boot stage, with ability to load and boot kernel to RAM via uart. Initramfs console in possible.
This way also allows you to use phone as daily driver during development, since storage is not touched
==== Building ====
* build u-boot.bin file. Follow u-boot docs installation section
* build mainline kernel 
** clone sources
** source /home/dzmitry/side/pmos/pmbootstrap/helpers/envkernel.sh
** make defconfig
** make
* assemble initramfs
* 
==== Installing ====
This section is useless for now, because currently there's no way to tell if something is alive, when you boot from the flash. 
See next section.
==== Booting kernel and getting console ====
Is performed with kexec-similar stuff for now. See guide for that method. Remember, you should have a cable from in `UART USB-debug cable schematic` section of Samsung_Galaxy_A5_2017_(samsung-a5y17lte)#Notes, and 1.8V compatible uart adapter
* Download prebuilt twrp image, with kexec and manual muic switching support
* Boot into twrp 
* Connect uart-usb cable
* Switch muic uart on usb, and run u-boot.
** go to Advanced -> Terminal
** run /exec.sh command. It will switch uart on usb, load u-boot(it's included in twrp image) in RAM, and run it. 
** You are in u-boot console now ;) 
* Load u-boot payload via kermit (you may use my high speed version for linux at 921600bps)
** in u-boot prompt run loadb 0x90000000
* in u-boot prompt run bootm 0x90000000 command