[POWERPC] Document describing mpc52xx device tree binding conventions

MPC52xx Device Tree Bindings

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

(c) 2006 Secret Lab Technologies Ltd

Grant Likely <grant.likely at secretlab.ca>

I - Introduction

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

Boards supported by the arch/powerpc architecture require device tree be

passed by the boot loader to the kernel at boot time.  The device tree

describes what devices are present on the board and how they are

connected.  The device tree can either be passed as a binary blob (as

described in Documentation/powerpc/booting-without-of.txt), or passed

by Open Firmare (IEEE 1275) compatible firmware using an OF compatible

client interface API.

This document specifies the requirements on the device-tree for mpc52xx

based boards.  These requirements are above and beyond the details

specified in either the OpenFirmware spec or booting-without-of.txt

All new mpc52xx-based boards are expected to match this document.  In

cases where this document is not sufficient to support a new board port,

this document should be updated as part of adding the new board support.

II - Philosophy

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

The core of this document is naming convention.  The whole point of

defining this convention is to reduce or eliminate the number of

special cases required to support a 52xx board.  If all 52xx boards

follow the same convention, then generic 52xx support code will work

rather than coding special cases for each new board.

This section tries to capture the thought process behind why the naming

convention is what it is.

1. Node names

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

There is strong convention/requirements already established for children

of the root node.  'cpus' describes the processor cores, 'memory'

describes memory, and 'chosen' provides boot configuration.  Other nodes

are added to describe devices attached to the processor local bus.

Following convention already established with other system-on-chip

processors, MPC52xx boards must have an 'soc5200' node as a child of the

root node.

The soc5200 node holds child nodes for all on chip devices.  Child nodes

are typically named after the configured function.  ie. the FEC node is

named 'ethernet', and a PSC in uart mode is named 'serial'.

2. device_type property

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

similar to the node name convention above; the device_type reflects the

configured function of a device.  ie. 'serial' for a uart and 'spi' for

an spi controller.  However, while node names *should* reflect the

configured function, device_type *must* match the configured function

exactly.

3. compatible property

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

Since device_type isn't enough to match devices to drivers, there also

needs to be a naming convention for the compatible property.  Compatible

is an list of device descriptions sorted from specific to generic.  For

the mpc52xx, the required format for each compatible value is

<chip>-<device>[-<mode>].  At the minimum, the list shall contain two

items; the first specifying the exact chip, and the second specifying

mpc52xx for the chip.

ie. ethernet on mpc5200b: compatible = "mpc5200b-ethernet\0mpc52xx-ethernet"

The idea here is that most drivers will match to the most generic field

in the compatible list (mpc52xx-*), but can also test the more specific

field for enabling bug fixes or extra features.

Modal devices, like PSCs, also append the configured function to the

end of the compatible field.  ie. A PSC in i2s mode would specify

"mpc52xx-psc-i2s", not "mpc52xx-i2s".  This convention is chosen to

avoid naming conflicts with non-psc devices providing the same

function.  For example, "mpc52xx-spi" and "mpc52xx-psc-spi" describe

the mpc5200 simple spi device and a PSC spi mode respectively.

If the soc device is more generic and present on other SOCs, the

compatible property can specify the more generic device type also.

ie. mscan: compatible = "mpc5200-mscan\0mpc52xx-mscan\0fsl,mscan";

At the time of writing, exact chip may be either 'mpc5200' or

'mpc5200b'.

Device drivers should always try to match as generically as possible.

III - Structure

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

The device tree for an mpc52xx board follows the structure defined in

booting-without-of.txt with the following additional notes:

0) the root node

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

Typical root description node; see booting-without-of

1) The cpus node

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

The cpus node follows the basic layout described in booting-without-of.

The bus-frequency property holds the XLB bus frequency

The clock-frequency property holds the core frequency

2) The memory node

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

Typical memory description node; see booting-without-of.

3) The soc5200 node

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

This node describes the on chip SOC peripherals.  Every mpc52xx based

board will have this node, and as such there is a common naming

convention for SOC devices.

Required properties:

name			type		description

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

device_type		string		must be "soc"

ranges			int		should be <0 baseaddr baseaddr+10000>

reg			int		must be <baseaddr 10000>

Recommended properties:

name			type		description

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

compatible		string		should be "<chip>-soc\0mpc52xx-soc"

					ie. "mpc5200b-soc\0mpc52xx-soc"

#interrupt-cells	int		must be <3>.  If it is not defined

					here then it must be defined in every

					soc device node.

bus-frequency		int		IPB bus frequency in HZ.  Clock rate

					used by most of the soc devices.

					Defining it here avoids needing it

					added to every device node.

4) soc5200 child nodes

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

Any on chip SOC devices available to Linux must appear as soc5200 child nodes.

Note: in the tables below, '*' matches all <chip> values.  ie.

*-pic would translate to "mpc5200-pic\0mpc52xx-pic"

Required soc5200 child nodes:

name		device_type		compatible	Description

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

cdm@<addr>	cdm			*-cmd		Clock Distribution

pic@<addr>	interrupt-controller	*-pic		need an interrupt

							controller to boot

bestcomm@<addr>	dma-controller		*-bestcomm	52xx pic also requires

							the bestcomm device

Recommended soc5200 child nodes; populate as needed for your board

name		device_type	compatible	Description

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

gpt@<addr>	gpt		*-gpt		General purpose timers

rtc@<addr>	rtc		*-rtc		Real time clock

mscan@<addr>	mscan		*-mscan		CAN bus controller

pci@<addr>	pci		*-pci		PCI bridge

serial@<addr>	serial		*-psc-uart	PSC in serial mode

i2s@<addr>	i2s		*-psc-i2s	PSC in i2s mode

ac97@<addr>	ac97		*-psc-ac97	PSC in ac97 mode

spi@<addr>	spi		*-psc-spi	PSC in spi mode

irda@<addr>	irda		*-psc-irda	PSC in IrDA mode

spi@<addr>	spi		*-spi		MPC52xx spi device

ethernet@<addr>	network		*-fec		MPC52xx ethernet device

ata@<addr>	ata		*-ata		IDE ATA interface

i2c@<addr>	i2c		*-i2c		I2C controller

usb@<addr>	usb-ohci-be	*-ohci,ohci-be	USB controller

xlb@<addr>	xlb		*-xlb		XLB arbritrator

IV - Extra Notes

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

1. Interrupt mapping

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

The mpc52xx pic driver splits hardware IRQ numbers into two levels.  The

split reflects the layout of the PIC hardware itself, which groups

interrupts into one of three groups; CRIT, MAIN or PERP.  Also, the

Bestcomm dma engine has it's own set of interrupt sources which are

cascaded off of peripheral interrupt 0, which the driver interprets as a

fourth group, SDMA.

The interrupts property for device nodes using the mpc52xx pic consists

of three cells; <L1 L2 level>

    L1 := [CRIT=0, MAIN=1, PERP=2, SDMA=3]

    L2 := interrupt number; directly mapped from the value in the

          "ICTL PerStat, MainStat, CritStat Encoded Register"

    level := [LEVEL_HIGH=0, EDGE_RISING=1, EDGE_FALLING=2, LEVEL_LOW=3]