dt-bindings: arm: fsl: add scu binding doc

NXP i.MX System Controller Firmware (SCFW)

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

The System Controller Firmware (SCFW) is a low-level system function

which runs on a dedicated Cortex-M core to provide power, clock, and

resource management. It exists on some i.MX8 processors. e.g. i.MX8QM

(QM, QP), and i.MX8QX (QXP, DX).

The AP communicates with the SC using a multi-ported MU module found

in the LSIO subsystem. The current definition of this MU module provides

5 remote AP connections to the SC to support up to 5 execution environments

(TZ, HV, standard Linux, etc.). The SC side of this MU module interfaces

with the LSIO DSC IP bus. The SC firmware will communicate with this MU

using the MSI bus.

System Controller Device Node:

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

The scu node with the following properties shall be under the /firmware/ node.

Required properties:

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

- compatible:	should be "fsl,imx-scu".

- mbox-names:	should include "tx0", "tx1", "tx2", "tx3",

			       "rx0", "rx1", "rx2", "rx3".

- mboxes:	List of phandle of 4 MU channels for tx and 4 MU channels

		for rx. All 8 MU channels must be in the same MU instance.

		Cross instances are not allowed. The MU instance can only

		be one of LSIO MU0~M4 for imx8qxp and imx8qm. Users need

		to make sure use the one which is not conflict with other

		execution environments. e.g. ATF.

		Note:

		Channel 0 must be "tx0" or "rx0".

		Channel 1 must be "tx1" or "rx1".

		Channel 2 must be "tx2" or "rx2".

		Channel 3 must be "tx3" or "rx3".

		e.g.

		mboxes = <&lsio_mu1 0 0

			  &lsio_mu1 0 1

			  &lsio_mu1 0 2

			  &lsio_mu1 0 3

			  &lsio_mu1 1 0

			  &lsio_mu1 1 1

			  &lsio_mu1 1 2

			  &lsio_mu1 1 3>;

		See Documentation/devicetree/bindings/mailbox/fsl,mu.txt

		for detailed mailbox binding.

i.MX SCU Client Device Node:

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

Client nodes are maintained as children of the relevant IMX-SCU device node.

Power domain bindings based on SCU Message Protocol

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

This binding for the SCU power domain providers uses the generic power

domain binding[2].

Required properties:

- compatible:		Should be "fsl,scu-pd".

- #address-cells:	Should be 1.

- #size-cells:		Should be 0.

Required properties for power domain sub nodes:

- #power-domain-cells:	Must be 0.

Optional Properties:

- reg:			Resource ID of this power domain.

			No exist means uncontrollable by user.

			See detailed Resource ID list from:

			include/dt-bindings/power/imx-rsrc.h

- power-domains:	phandle pointing to the parent power domain.

Clock bindings based on SCU Message Protocol

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

This binding uses the common clock binding[1].

Required properties:

- compatible:		Should be "fsl,imx8qxp-clock".

- #clock-cells:		Should be 1. Contains the Clock ID value.

- clocks:		List of clock specifiers, must contain an entry for

			each required entry in clock-names

- clock-names:		Should include entries "xtal_32KHz", "xtal_24MHz"

The clock consumer should specify the desired clock by having the clock

ID in its "clocks" phandle cell.

See the full list of clock IDs from:

include/dt-bindings/clock/imx8qxp-clock.h

Pinctrl bindings based on SCU Message Protocol

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

This binding uses the i.MX common pinctrl binding[3].

Required properties:

- compatible:		Should be "fsl,imx8qxp-iomuxc".

Required properties for Pinctrl sub nodes:

- fsl,pins:		Each entry consists of 3 integers which represents

			the mux and config setting for one pin. The first 2

			integers <pin_id mux_mode> are specified using a

			PIN_FUNC_ID macro, which can be found in

			<dt-bindings/pinctrl/pads-imx8qxp.h>.

			The last integer CONFIG is the pad setting value like

			pull-up on this pin.

			Please refer to i.MX8QXP Reference Manual for detailed

			CONFIG settings.

[1] Documentation/devicetree/bindings/clock/clock-bindings.txt

[2] Documentation/devicetree/bindings/power/power_domain.txt

[3] Documentation/devicetree/bindings/pinctrl/fsl,imx-pinctrl.txt

Example (imx8qxp):

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

lsio_mu1: mailbox@5d1c0000 {

	...

	#mbox-cells = <2>;

};

firmware {

	scu {

		compatible = "fsl,imx-scu";

		mbox-names = "tx0", "tx1", "tx2", "tx3",

			     "rx0", "rx1", "rx2", "rx3";

		mboxes = <&lsio_mu1 0 0

			  &lsio_mu1 0 1

			  &lsio_mu1 0 2

			  &lsio_mu1 0 3

			  &lsio_mu1 1 0

			  &lsio_mu1 1 1

			  &lsio_mu1 1 2

			  &lsio_mu1 1 3>;

		clk: clk {

			compatible = "fsl,imx8qxp-clk";

			#clock-cells = <1>;

		};

		iomuxc {

			compatible = "fsl,imx8qxp-iomuxc";

			pinctrl_lpuart0: lpuart0grp {

				fsl,pins = <

					SC_P_UART0_RX_ADMA_UART0_RX	0x06000020

					SC_P_UART0_TX_ADMA_UART0_TX	0x06000020

				>;

			};

			...

		};

		imx8qx-pm {

			compatible = "fsl,scu-pd";

			#address-cells = <1>;

			#size-cells = <0>;

			pd_dma: dma-power-domain {

				#power-domain-cells = <0>;

				pd_dma_lpuart0: dma-lpuart0@57 {

					reg = <SC_R_UART_0>;

					#power-domain-cells = <0>;

					power-domains = <&pd_dma>;

				};

				...

			};

			...

		};

	};

};

serial@5a060000 {

	...

	pinctrl-names = "default";

	pinctrl-0 = <&pinctrl_lpuart0>;

	clocks = <&clk IMX8QXP_UART0_CLK>,

		 <&clk IMX8QXP_UART0_IPG_CLK>;

	clock-names = "per", "ipg";

	power-domains = <&pd_dma_lpuart0>;

};