board: samsung: add support for Galaxy A series of 2017 (a5y17lte)

Samsung Galaxy A3, A5, A7 (2017) - middle class Samsung smartphones.
U-boot can be used as chain-loaded bootloader to gain control
on booting vanilla linux(and possibly others) kernels

Signed-off-by: Dzmitry Sankouski <dsankouski@gmail.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>

3 files changed, 104 insertions, 0 deletions

diff --git a/doc/board/index.rst b/doc/board/index.rst
index 1b93ced..74ea33e 100644
--- a/doc/board/index.rst
+++ b/doc/board/index.rst
@@ -23,6 +23,7 @@ Board-specific doc
    openpiton/index
    qualcomm/index
    rockchip/index
+   samsung/index
    siemens/index
    sifive/index
    sipeed/index
diff --git a/doc/board/samsung/axy17lte.rst b/doc/board/samsung/axy17lte.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+.. sectionauthor:: Dzmitry Sankouski <dsankouski@gmail.com>
+
+Samsung 2017 A series phones
+============================
+
+About this
+----------
+This document describes the information about Samsung A(7/5/3) 2017 midrange
+phones and u-boot usage steps.
+
+U-Boot can be used as a chain-loaded bootloader to replace Samsung's original SBOOT bootloader.
+It is loaded as an Android boot image through SBOOT.
+
+Phone specs
+-----------
+A3 (SM-320) (a3y17lte)
+^^^^^^^^^^^^^^^^^^^^^^
+- 4.7 AMOLED display
+- Exynos 7870 SoC
+- 16GB flash
+- 2GB RAM
+
+.. A3 2017 wiki page: https://en.wikipedia.org/wiki/Samsung_Galaxy_A3_(2017)
+
+A5 (SM-520) (a5y17lte)
+^^^^^^^^^^^^^^^^^^^^^^
+- 5.2 AMOLED display
+- Exynos 7880 SoC
+- 32GB flash
+- 3GB RAM
+
+.. A5 2017 wiki page: https://en.wikipedia.org/wiki/Samsung_Galaxy_A5_(2017)
+
+A7 (SM-720) (a5y17lte)
+^^^^^^^^^^^^^^^^^^^^^^
+- 5.7 AMOLED display
+- Exynos 7880 SoC
+- 32GB flash
+- 3GB RAM
+
+.. A7 2017 wiki page: https://en.wikipedia.org/wiki/Samsung_Galaxy_A7_(2017)
+
+Installation
+------------
+
+Building u-boot
+^^^^^^^^^^^^^^^
+
+First, setup ``CROSS_COMPILE`` for aarch64.
+Then, build U-Boot for your phone, for example ``a5y17lte``::
+
+  $ export CROSS_COMPILE=<aarch64 toolchain prefix>
+  $ make a5y17lte_defconfig
+  $ make
+
+This will build ``u-boot.bin`` in the configured output directory.
+
+Payload
+^^^^^^^
+What is a payload?
+""""""""""""""""""
+A payload file is a file to be used instead of linux kernel in android boot image.
+This file will be loaded into memory, and executed by SBOOT,
+and is therefore SBOOT's payload.
+It may be pure u-boot (with loading u-boot's payload from flash in mind),
+or u-boot + u-boot's payload.
+
+It should be kept in mind, that SBOOT binary patches it's payload after loading
+in address range 0x401f8550-0x401f9280. Given SBOOT loads payload to 0x40001000,
+a range of 0x1f7550-0x1f8280 (2061648-2065024) in a payload file
+will be corrupted after loading to RAM.
+
+Creating payload file
+"""""""""""""""""""""
+- Assemble FIT image for your kernel
+- Create a file for u-boot payload ``touch sboot-payload``
+- Write zeroes till 0x200000 address to be sure SBOOT won't corrupt your info
+  ``dd if=/dev/zero of=sboot-payload bs=$((0x200000)) count=1``
+- Write u-boot to the start of the payload ``dd if=<u-boot.bin path> of=sboot-payload``
+- Write FIT image to payload from 0x200000 address
+  ``dd if=<FIT image path> of=sboot-payload seek=1 bs=2M``
+
+Creating android boot image
+"""""""""""""""""""""""""""
+Once payload created, it's time for android image::
+
+  mkbootimg --base 0x40000000 --kernel_offset 0x00000000 --ramdisk_offset 0x01000000 --tags_offset 0x00000100 --pagesize 2048 --second_offset 0x00f00000 --kernel <sboot-payload path> -o uboot.img
+
+Note, that stock Samsung bootloader ignores offsets, set in mkbootimg.
+
+Flashing
+""""""""
+Flash like regular android boot image.
diff --git a/doc/board/samsung/index.rst b/doc/board/samsung/index.rst
new file mode 100644
index 0000000..c904372
--- /dev/null
+++ b/doc/board/samsung/index.rst
@@ -0,0 +1,9 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Samsung
+========
+
+.. toctree::
+   :maxdepth: 2
+
+   axy17lte