ARM: keystone: add documentation for SoCs and EVMs

		TI Keystone Linux Overview

		--------------------------

Introduction

------------

Keystone range of SoCs are based on ARM Cortex-A15 MPCore Processors

and c66x DSP cores. This document describes essential information required

for users to run Linux on Keystone based EVMs from Texas Instruments.

Following SoCs  & EVMs are currently supported:-

------------ K2HK SoC and EVM --------------------------------------------------

a.k.a Keystone 2 Hawking/Kepler SoC

TCI6636K2H & TCI6636K2K: See documentation at

	http://www.ti.com/product/tci6638k2k

	http://www.ti.com/product/tci6638k2h

EVM:

http://www.advantech.com/Support/TI-EVM/EVMK2HX_sd.aspx

------------ K2E SoC and EVM ---------------------------------------------------

a.k.a Keystone 2 Edison SoC

K2E  -  66AK2E05: See documentation at

	http://www.ti.com/product/66AK2E05/technicaldocuments

EVM:

https://www.einfochips.com/index.php/partnerships/texas-instruments/k2e-evm.html

------------ K2L SoC and EVM ---------------------------------------------------

a.k.a Keystone 2 Lamarr SoC

K2L  -  TCI6630K2L: See documentation at

	http://www.ti.com/product/TCI6630K2L/technicaldocuments

EVM:

https://www.einfochips.com/index.php/partnerships/texas-instruments/k2l-evm.html

Configuration

-------------

All of the K2 SoCs/EVMs share a common defconfig, keystone_defconfig and same

image is used to boot on individual EVMs. The platform configuration is

specified through DTS. Following are the DTS used:-

	K2HK EVM : k2hk-evm.dts

	K2E EVM  : k2e-evm.dts

	K2L EVM  : k2l-evm.dts

The device tree documentation for the keystone machines are located at

        Documentation/devicetree/bindings/arm/keystone/keystone.txt

Known issues & workaround

-------------------------

Some of the device drivers used on keystone are re-used from that from

DaVinci and other TI SoCs. These device drivers may use clock APIs directly.

Some of the keystone specific drivers such as netcp uses run time power

management API instead to enable clock. As this API has limitations on

keystone, following workaround is needed to boot Linux.

   Add 'clk_ignore_unused' to the bootargs env variable in u-boot. Otherwise

   clock frameworks will try to disable clocks that are unused and disable

   the hardware. This is because netcp related power domain and clock

   domains are enabled in u-boot as run time power management API currently

   doesn't enable clocks for netcp due to a limitation. This workaround is

   expected to be removed in the future when proper API support becomes

   available. Until then, this work around is needed.

Document Author

---------------

Murali Karicheri <m-karicheri2@ti.com>

Copyright 2015 Texas Instruments