ARM: at91/Documentation: add a README for Atmel SoCs

ARM Atmel SoCs (aka AT91)

=========================

Introduction

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

This document gives useful information about the ARM Atmel SoCs that are

currently supported in Linux Mainline (you know, the one on kernel.org).

It is important to note that the Atmel | SMART ARM-based MPU product line is

historically named "AT91" or "at91" throughout the Linux kernel development

process even if this product prefix has completely disappeared from the

official Atmel product name. Anyway, files, directories, git trees,

git branches/tags and email subject always contain this "at91" sub-string.

AT91 SoCs

---------

Documentation and detailled datasheet for each product are available on

the Atmel website: http://www.atmel.com.

  Flavors:

    * ARM 920 based SoC

      - at91rm9200

        + Datasheet

          http://www.atmel.com/Images/doc1768.pdf

    * ARM 926 based SoCs

      - at91sam9260

        + Datasheet

          http://www.atmel.com/Images/doc6221.pdf

      - at91sam9xe

        + Datasheet

          http://www.atmel.com/Images/Atmel-6254-32-bit-ARM926EJ-S-Embedded-Microprocessor-SAM9XE_Datasheet.pdf

      - at91sam9261

        + Datasheet

          http://www.atmel.com/Images/doc6062.pdf

      - at91sam9263

        + Datasheet

          http://www.atmel.com/Images/Atmel_6249_32-bit-ARM926EJ-S-Microcontroller_SAM9263_Datasheet.pdf

      - at91sam9rl

        + Datasheet

          http://www.atmel.com/Images/doc6289.pdf

      - at91sam9g20

        + Datasheet

          http://www.atmel.com/Images/doc6384.pdf

      - at91sam9g45 family

        - at91sam9g45

        - at91sam9g46

        - at91sam9m10

        - at91sam9m11 (device superset)

        + Datasheet

          http://www.atmel.com/Images/Atmel-6437-32-bit-ARM926-Embedded-Microprocessor-SAM9M11_Datasheet.pdf

      - at91sam9x5 family (aka "The 5 series")

        - at91sam9g15

        - at91sam9g25

        - at91sam9g35

        - at91sam9x25

        - at91sam9x35

        + Datasheet (can be considered as covering the whole family)

          http://www.atmel.com/Images/Atmel_11055_32-bit-ARM926EJ-S-Microcontroller_SAM9X35_Datasheet.pdf

      - at91sam9n12

        + Datasheet

          http://www.atmel.com/Images/Atmel_11063_32-bit-ARM926EJ-S-Microcontroller_SAM9N12CN11CN12_Datasheet.pdf

    * ARM Cortex-A5 based SoCs

      - sama5d3 family

        - sama5d31

        - sama5d33

        - sama5d34

        - sama5d35

        - sama5d36 (device superset)

        + Datasheet

          http://www.atmel.com/Images/Atmel-11121-32-bit-Cortex-A5-Microcontroller-SAMA5D3_Datasheet.pdf

    * ARM Cortex-A5 + NEON based SoCs

      - sama5d4 family

        - sama5d41

        - sama5d42

        - sama5d43

        - sama5d44 (device superset)

        + Datasheet

          http://www.atmel.com/Images/Atmel-11238-32-bit-Cortex-A5-Microcontroller-SAMA5D4_Datasheet.pdf

Linux kernel information

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

Linux kernel mach directory: arch/arm/mach-at91

MAINTAINERS entry is: "ARM/ATMEL AT91RM9200 AND AT91SAM ARM ARCHITECTURES"

Device Tree for AT91 SoCs and boards

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

All AT91 SoCs are converted to Device Tree. Since Linux 3.19, these products

must use this method to boot the Linux kernel.

Work In Progress statement:

Device Tree files and Device Tree bindings that apply to AT91 SoCs and boards are

considered as "Unstable". To be completely clear, any at91 binding can change at

any time. So, be sure to use a Device Tree Binary and a Kernel Image generated from

the same source tree.

Please refer to the Documentation/devicetree/bindings/ABI.txt file for a

definition of a "Stable" binding/ABI.

This statement will be removed by AT91 MAINTAINERS when appropriate.

Naming conventions and best practice:

- SoCs Device Tree Source Include files are named after the official name of

  the product (at91sam9g20.dtsi or sama5d33.dtsi for instance).

- Device Tree Source Include files (.dtsi) are used to collect common nodes that can be

  shared across SoCs or boards (sama5d3.dtsi or at91sam9x5cm.dtsi for instance).

  When collecting nodes for a particular peripheral or topic, the identifier have to

  be placed at the end of the file name, separated with a "_" (at91sam9x5_can.dtsi

  or sama5d3_gmac.dtsi for example).

- board Device Tree Source files (.dts) are prefixed by the string "at91-" so

  that they can be identified easily. Note that some files are historical exceptions

  to this rule (sama5d3[13456]ek.dts, usb_a9g20.dts or animeo_ip.dts for example).