board: samsung: Add support for E850-96 board

Add support for WinLink E850-96 board [1]. It's based on Exynos850 SoC
and follows 96boards specification, so it's compatible with 96boards
mezzanine boards [2]. This patch enables next features:

  * Serial console
  * USI
  * PMU (muxing AP UART path)
  * Pinctrl
  * Clocks
  * Timer (ARMv8 architected)
  * Reset control

It's quite a minimal enablement. Features like MMC, USB and Ethernet
will be enabled later.

The rationale for config values is as follows:

  * TEXT_BASE = 0xf8800000

    That's where BL2 loads the U-Boot payload, so TEXT_BASE must be
    exactly this value. Overall the memory map is designed in a way to
    keep the bootloader in the upper 128 MiB area of RAM, which is
    0xf8000000..0xffffffff. That includes bootloader's code, stack,
    data, heap, MMU tables, etc. All the memory below that 128 MiB chunk
    can be used for storing boot images (0x80000000..0xf8000000).

  * CUSTOM_SYS_INIT_SP_ADDR = 0xf8c00000

    Just 4 MiB above the TEXT_BASE address, to leave enough space for
    U-Boot code and stack itself (grows downwards).

  * SYS_LOAD_ADDR = 0x80000000

    The beginning of RAM. That's where Linux kernel image must be
    loaded.

  * SYS_MALLOC_LEN = 0x81f000

    8 MiB for malloc() + ENV_SIZE (128 KiB)

  * SYS_MALLOC_F_LEN = 0x4000

    Increase malloc() pool size available before relocation from 8 KiB
    (default) to 16 KiB. Otherwise "alloc space exhausted" message
    appears in U-Boot log during board_init_f() stage. There are next
    reasons for doing so:

      1. Having "bootph-all" flags in some dts nodes leads to binding
         those during pre-relocation stage, and binding (DM) uses
         dynamic memory allocation
      2. clk-exynos850 driver uses CCF clocks, which in turn use dynamic
         memory allocation

Device tree file was imported from Linux kernel. All nodes and boot
phase flags added in exynos850-e850-96-u-boot.dtsi are only needed to
enable serial console:

  * oscclk -> cmu_top -> cmu_peri: generate UART/USI clocks
  * pinctrl_alive and uart1_pins: needed to mux UART pins
  * pmu_system_controller: configures AP UART path to uart1_pins
  * usi_uart: configures USI block to operate as a UART protocol
  * serial_0: enables serial console (UART)

[1] https://www.96boards.org/product/e850-96b/
[2] https://www.96boards.org/products/mezzanine/

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>

doc/board/samsung/e850-96.rst

@@ -0,0 +1,87 @@
+.. SPDX-License-Identifier: GPL-2.0+
+.. sectionauthor:: Sam Protsenko <semen.protsenko@linaro.org>
+
+WinLink E850-96 board
+=====================
+
+Overview
+--------
+
+WinLink's E850-96 board [1]_ is based on Samsung Exynos850 SoC and follows
+96Boards Consumer Edition specification [2]_. That makes it possible to use
+96Boards mezzanine boards [3]_ along with it. It's an open-hardware board and
+the hardware design files [4]_ were published, along with the supported
+software [5]_ and related documentation.
+
+U-Boot can be used on E850-96 instead of the original Samsung LittleKernel based
+bootloader [6]_. Because FWBL1 [7]_ doesn't verify bootloader's signature, there
+is no need to sign a U-Boot binary. That means U-Boot binary can be flashed into
+``bootloader`` partition (instead of LittleKernel bootloader) and it will just
+work.
+
+Because BL2 bootloader already sets up DRAM and runs the final bootloader
+(U-Boot) from DRAM, there is no need in U-Boot SPL. It's enough to have only
+U-Boot proper (``u-boot.bin``).
+
+Boot Flow
+---------
+
+The boot path for Exynos850 is shown on the figure below.
+
+.. image:: img/exynos850-boot-architecture.svg
+  :alt: Exynos850 SoC boot flow
+
+Legend:
+
+* ``BL0``: Boot ROM code
+* ``BL1``: Software part of Boot ROM
+* ``EPBL``: Exynos Primary Boot Loader
+* ``BL2``: Initializes CMU and DRAM and runs the final bootloader
+* ``Bootloader``: Final bootloader (e.g. U-Boot); also called BL33 in terms of
+  ARM boot flow
+* ``EL3_MON``: EL3 monitor (trusted firmware, handles SMC calls); also called
+  BL31 in terms of ARM boot flow
+* ``LDFW``: Loadable Firmware
+
+Build Procedure
+---------------
+
+.. warning::
+  At the moment both eMMC and USB features are not enabled in U-Boot. Flashing
+  U-Boot binary **WILL** effectively brick your board. The ``dltool`` [8]_ can
+  be used then to perform USB boot and flash LittleKernel bootloader binary [7]_
+  to unbrick and revive the board. Flashing U-Boot binary might be helpful for
+  developers or anybody who want to check current state of U-Boot enablement on
+  E850-96 (which is mostly serial console and related blocks).
+
+Build U-Boot binary from source code (using AArch64 baremetal GCC toolchain):
+
+.. prompt:: bash $
+
+  export PATH=<toolchain path>/bin:$PATH
+  export CROSS_COMPILE=<toolchain prefix>
+  make e850-96_defconfig
+  make
+
+Boot E850-96 board into fastboot mode as described in board software doc [9]_,
+and flash U-Boot binary into ``bootloader`` eMMC partition:
+
+.. prompt:: bash $
+
+  fastboot flash bootloader u-boot.bin
+  fastboot reboot
+
+U-Boot will boot up to the shell.
+
+References
+----------
+
+.. [1] https://www.96boards.org/product/e850-96b/
+.. [2] https://www.96boards.org/products/ce/
+.. [3] https://www.96boards.org/products/mezzanine/
+.. [4] https://www.96boards.org/documentation/consumer/e850-96b/hardware-docs/
+.. [5] https://gitlab.com/Linaro/96boards/e850-96/
+.. [6] https://gitlab.com/Linaro/96boards/e850-96/lk
+.. [7] https://gitlab.com/Linaro/96boards/e850-96/images
+.. [8] https://gitlab.com/Linaro/96boards/e850-96/tools/dltool
+.. [9] https://gitlab.com/Linaro/96boards/e850-96/doc

doc/board/samsung/index.rst

@@ -7,3 +7,4 @@ Samsung
    :maxdepth: 2
 
    axy17lte
+   e850-96