dt-bindings: i3c: Document core bindings

Generic device tree bindings for I3C busses

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

This document describes generic bindings that should be used to describe I3C

busses in a device tree.

Required properties

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

- #address-cells  - should be <3>. Read more about addresses below.

- #size-cells     - should be <0>.

- compatible      - name of the I3C master controller driving the I3C bus

For other required properties e.g. to describe register sets,

clocks, etc. check the binding documentation of the specific driver.

The node describing an I3C bus should be named i3c-master.

Optional properties

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

These properties may not be supported by all I3C master drivers. Each I3C

master bindings should specify which of them are supported.

- i3c-scl-hz: frequency of the SCL signal used for I3C transfers.

	      When undefined the core sets it to 12.5MHz.

- i2c-scl-hz: frequency of the SCL signal used for I2C transfers.

	      When undefined, the core looks at LVR (Legacy Virtual Register)

	      values of I2C devices described in the device tree to determine

	      the maximum I2C frequency.

I2C devices

===========

Each I2C device connected to the bus should be described in a subnode. All

properties described in Documentation/devicetree/bindings/i2c/i2c.txt are

valid here, but several new properties have been added.

New constraint on existing properties:

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

- reg: contains 3 cells

  + first cell : still encoding the I2C address

  + second cell: shall be 0

  + third cell: shall encode the I3C LVR (Legacy Virtual Register)

	bit[31:8]: unused/ignored

	bit[7:5]: I2C device index. Possible values

	* 0: I2C device has a 50 ns spike filter

	* 1: I2C device does not have a 50 ns spike filter but supports high

	     frequency on SCL

	* 2: I2C device does not have a 50 ns spike filter and is not tolerant

	     to high frequencies

	* 3-7: reserved

	bit[4]: tell whether the device operates in FM (Fast Mode) or FM+ mode

	* 0: FM+ mode

	* 1: FM mode

	bit[3:0]: device type

	* 0-15: reserved

The I2C node unit-address should always match the first cell of the reg

property: <device-type>@<i2c-address>.

I3C devices

===========

All I3C devices are supposed to support DAA (Dynamic Address Assignment), and

are thus discoverable. So, by default, I3C devices do not have to be described

in the device tree.

This being said, one might want to attach extra resources to these devices,

and those resources may have to be described in the device tree, which in turn

means we have to describe I3C devices.

Another use case for describing an I3C device in the device tree is when this

I3C device has a static I2C address and we want to assign it a specific I3C

dynamic address before the DAA takes place (so that other devices on the bus

can't take this dynamic address).

The I3C device should be names <device-type>@<static-i2c-address>,<i3c-pid>,

where device-type is describing the type of device connected on the bus

(gpio-controller, sensor, ...).

Required properties

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

- reg: contains 3 cells

  + first cell : encodes the static I2C address. Should be 0 if the device does

		 not have one (0 is not a valid I2C address).

  + second and third cells: should encode the ProvisionalID. The second cell

			    contains the manufacturer ID left-shifted by 1.

			    The third cell contains ORing of the part ID

			    left-shifted by 16, the instance ID left-shifted

			    by 12 and the extra information. This encoding is

			    following the PID definition provided by the I3C

			    specification.

Optional properties

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

- assigned-address: dynamic address to be assigned to this device. This

		    property is only valid if the I3C device has a static

		    address (first cell of the reg property != 0).

Example:

	i3c-master@d040000 {

		compatible = "cdns,i3c-master";

		clocks = <&coreclock>, <&i3csysclock>;

		clock-names = "pclk", "sysclk";

		interrupts = <3 0>;

		reg = <0x0d040000 0x1000>;

		#address-cells = <3>;

		#size-cells = <0>;

		i2c-scl-hz = <100000>;

		/* I2C device. */

		nunchuk: nunchuk@52 {

			compatible = "nintendo,nunchuk";

			reg = <0x52 0x0 0x10>;

		};

		/* I3C device with a static I2C address. */

		thermal_sensor: sensor@68,39200144004 {

			reg = <0x68 0x392 0x144004>;

			assigned-address = <0xa>;

		};

		/*

		 * I3C device without a static I2C address but requiring

		 * resources described in the DT.

		 */

		sensor@0,39200154004 {

			reg = <0x0 0x392 0x154004>;

			clocks = <&clock_provider 0>;

		};

	};