doc: ti: Add readme for AM62x SK

Add info of boot flow and build steps for AM62x SK.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Bryan Brattlof <bb@ti.com>
diff --git a/doc/board/ti/am62x_sk.rst b/doc/board/ti/am62x_sk.rst
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+.. SPDX-License-Identifier: GPL-2.0+ OR BSD-3-Clause
+.. sectionauthor:: Vignesh Raghavendra <vigneshr@ti.com>
+
+Texas Instruments AM62 Platforms
+================================
+
+Introduction:
+-------------
+The AM62 SoC family is the follow on AM335x built on the K3 Multicore
+SoC architecture platform, providing ultra-low-power modes, dual
+display, multi-sensor edge compute, security and other BOM-saving
+integrations.  The AM62 SoC targets a broad market to enable
+applications such as Industrial HMI, PLC/CNC/Robot control, Medical
+Equipment, Building Automation, Appliances and more.
+
+Some highlights of this SoC are:
+
+* Quad-Cortex-A53s (running up to 1.4GHz) in a single cluster.
+  Pin-to-pin compatible options for single and quad core are available.
+* Cortex-M4F for general-purpose or safety usage.
+* Dual display support, providing 24-bit RBG parallel interface and
+  OLDI/LVDS-4 Lane x2, up to 200MHz pixel clock support for 2K display
+  resolution.
+* Selectable GPU support, up to 8GFLOPS, providing better user experience
+  in 3D graphic display case and Android.
+* PRU(Programmable Realtime Unit) support for customized programmable
+  interfaces/IOs.
+* Integrated Giga-bit Ethernet switch supporting up to a total of two
+  external ports (TSN capable).
+* 9xUARTs, 5xSPI, 6xI2C, 2xUSB2, 3xCAN-FD, 3x eMMC and SD, GPMC for
+  NAND/FPGA connection, OSPI memory controller, 3xMcASP for audio,
+  1x CSI-RX-4L for Camera, eCAP/eQEP, ePWM, among other peripherals.
+* Dedicated Centralized System Controller for Security, Power, and
+  Resource Management.
+* Multiple low power modes support, ex: Deep sleep, Standby, MCU-only,
+  enabling battery powered system design.
+
+More details can be found in the Technical Reference Manual:
+https://www.ti.com/lit/pdf/spruiv7
+
+Boot Flow:
+----------
+Below is the pictorial representation of boot flow:
+
+.. code-block:: text
+
+ +------------------------------------------------------------------------+
+ |        TIFS            |      Main R5          |        A53            |
+ +------------------------------------------------------------------------+
+ |    +--------+          |                       |                       |
+ |    |  Reset |          |                       |                       |
+ |    +--------+          |                       |                       |
+ |         :              |                       |                       |
+ |    +--------+          |   +-----------+       |                       |
+ |    | *ROM*  |----------|-->| Reset rls |       |                       |
+ |    +--------+          |   +-----------+       |                       |
+ |    |        |          |         :             |                       |
+ |    |  ROM   |          |         :             |                       |
+ |    |services|          |         :             |                       |
+ |    |        |          |   +-------------+     |                       |
+ |    |        |          |   |  *R5 ROM*   |     |                       |
+ |    |        |          |   +-------------+     |                       |
+ |    |        |<---------|---|Load and auth|     |                       |
+ |    |        |          |   | tiboot3.bin |     |                       |
+ |    +--------+          |   +-------------+     |                       |
+ |    |        |<---------|---| Load sysfw  |     |                       |
+ |    |        |          |   | part to TIFS|     |                       |
+ |    |        |          |   | core        |     |                       |
+ |    |        |          |   +-------------+     |                       |
+ |    |        |          |         :             |                       |
+ |    |        |          |         :             |                       |
+ |    |        |          |         :             |                       |
+ |    |        |          |   +-------------+     |                       |
+ |    |        |          |   |  *R5 SPL*   |     |                       |
+ |    |        |          |   +-------------+     |                       |
+ |    |        |          |   |    DDR      |     |                       |
+ |    |        |          |   |   config    |     |                       |
+ |    |        |          |   +-------------+     |                       |
+ |    |        |          |   |    Load     |     |                       |
+ |    |        |          |   |  tispl.bin  |     |                       |
+ |    |        |          |   +-------------+     |                       |
+ |    |        |          |   |   Load R5   |     |                       |
+ |    |        |          |   |   firmware  |     |                       |
+ |    |        |          |   +-------------+     |                       |
+ |    |        |<---------|---| Start A53   |     |                       |
+ |    |        |          |   | and jump to |     |                       |
+ |    |        |          |   | DM fw image |     |                       |
+ |    |        |          |   +-------------+     |                       |
+ |    |        |          |                       |     +-----------+     |
+ |    |        |----------|-----------------------|---->| Reset rls |     |
+ |    |        |          |                       |     +-----------+     |
+ |    |  TIFS  |          |                       |          :            |
+ |    |Services|          |                       |     +-----------+     |
+ |    |        |<---------|-----------------------|---->|*ATF/OPTEE*|     |
+ |    |        |          |                       |     +-----------+     |
+ |    |        |          |                       |          :            |
+ |    |        |          |                       |     +-----------+     |
+ |    |        |<---------|-----------------------|---->| *A53 SPL* |     |
+ |    |        |          |                       |     +-----------+     |
+ |    |        |          |                       |     |   Load    |     |
+ |    |        |          |                       |     | u-boot.img|     |
+ |    |        |          |                       |     +-----------+     |
+ |    |        |          |                       |          :            |
+ |    |        |          |                       |     +-----------+     |
+ |    |        |<---------|-----------------------|---->| *U-Boot*  |     |
+ |    |        |          |                       |     +-----------+     |
+ |    |        |          |                       |     |  prompt   |     |
+ |    |        |----------|-----------------------|-----+-----------+-----|
+ |    +--------+          |                       |                       |
+ |                        |                       |                       |
+ +------------------------------------------------------------------------+
+
+- Here TIFS acts as master and provides all the critical services. R5/A53
+  requests TIFS to get these services done as shown in the above diagram.
+
+Sources:
+--------
+1. SYSFW:
+	Tree: git://git.ti.com/k3-image-gen/k3-image-gen.git
+	Branch: master
+
+2. ATF:
+	Tree: https://github.com/ARM-software/arm-trusted-firmware.git
+	Branch: master
+
+3. OPTEE:
+	Tree: https://github.com/OP-TEE/optee_os.git
+	Branch: master
+
+4. U-Boot:
+	Tree: https://source.denx.de/u-boot/u-boot
+	Branch: master
+
+5. TI Linux Firmware:
+	Tree: git://git.ti.com/processor-firmware/ti-linux-firmware.git
+	Branch: ti-linux-firmware
+
+Build procedure:
+----------------
+1. ATF:
+
+.. code-block:: text
+
+ $ make CROSS_COMPILE=aarch64-none-linux-gnu- ARCH=aarch64 PLAT=k3 TARGET_BOARD=lite SPD=opteed
+
+2. OPTEE:
+
+.. code-block:: text
+
+ $ make PLATFORM=k3 CFG_ARM64_core=y CROSS_COMPILE=arm-none-linux-gnueabihf- CROSS_COMPILE64=aarch64-none-linux-gnu-
+
+3. U-Boot:
+
+* 3.1 R5:
+
+.. code-block:: text
+
+ $ make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabihf- am62x_evm_r5_defconfig O=/tmp/r5
+ $ make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabihf- O=/tmp/r5
+ $ cd <k3-image-gen>
+ $ make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabihf- SOC=am62x SBL=/tmp/r5/spl/u-boot-spl.bin SYSFW_PATH=<path to ti-linux-firmware>/ti-sysfw/ti-fs-firmware-am62x-gp.bin
+
+Use the tiboot3.bin generated from last command
+
+* 3.2 A53:
+
+.. code-block:: text
+
+ $ make ARCH=arm CROSS_COMPILE=aarch64-none-linux-gnu- am62x_evm_a53_defconfig O=/tmp/a53
+ $ make ARCH=arm CROSS_COMPILE=aarch64-none-linux-gnu- ATF=<path to ATF dir>/build/k3/lite/release/bl31.bin TEE=<path to OPTEE OS dir>/out/arm-plat-k3/core/tee-pager_v2.bin DM=<path to ti-linux-firmware>/ti-dm/am62xx/ipc_echo_testb_mcu1_0_release_strip.xer5f O=/tmp/a53
+
+Target Images
+--------------
+Copy the below images to an SD card and boot:
+ - tiboot3.bin from step 3.1
+ - tispl.bin, u-boot.img from 3.2
+
+Image formats:
+--------------
+
+- tiboot3.bin:
+
+.. code-block:: text
+
+                +-----------------------+
+                |        X.509          |
+                |      Certificate      |
+                | +-------------------+ |
+                | |                   | |
+                | |        R5         | |
+                | |   u-boot-spl.bin  | |
+                | |                   | |
+                | +-------------------+ |
+                | |                   | |
+                | |TIFS with board cfg| |
+                | |                   | |
+                | +-------------------+ |
+                | |                   | |
+                | |                   | |
+                | |     FIT header    | |
+                | | +---------------+ | |
+                | | |               | | |
+                | | |   DTB 1...N   | | |
+                | | +---------------+ | |
+                | +-------------------+ |
+                +-----------------------+
+
+- tispl.bin
+
+.. code-block:: text
+
+                +-----------------------+
+                |                       |
+                |       FIT HEADER      |
+                | +-------------------+ |
+                | |                   | |
+                | |      A53 ATF      | |
+                | +-------------------+ |
+                | |                   | |
+                | |     A53 OPTEE     | |
+                | +-------------------+ |
+                | |                   | |
+                | |      R5 DM FW     | |
+                | +-------------------+ |
+                | |                   | |
+                | |      A53 SPL      | |
+                | +-------------------+ |
+                | |                   | |
+                | |   SPL DTB 1...N   | |
+                | +-------------------+ |
+                +-----------------------+