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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";
		include "gip3" if want to support general MU interrupt.
- mboxes:	List of phandle of 4 MU channels for tx, 4 MU channels for
		rx, and 1 optional MU channel for general interrupt.
		All 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".
		General interrupt rx channel must be "gip3".
		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
			  &lsio_mu1 3 3>;
		See Documentation/devicetree/bindings/mailbox/fsl,mu.yaml
		for detailed mailbox binding.

Note: Each mu which supports general interrupt should have an alias correctly
numbered in "aliases" node.
e.g.
aliases {
	mu1 = &lsio_mu1;
};

i.MX SCU Client Device Node:
============================================================

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

Watchdog bindings based on SCU Message Protocol
------------------------------------------------------------

Required properties:
- compatible: should be:
              "fsl,imx8qxp-sc-wdt"
              followed by "fsl,imx-sc-wdt";
Optional properties:
- timeout-sec: contains the watchdog timeout in seconds.

Example (imx8qxp):
-------------
aliases {
	mu1 = &lsio_mu1;
};

lsio_mu1: mailbox@5d1c0000 {
	...
	#mbox-cells = <2>;
};

firmware {
	scu {
		compatible = "fsl,imx-scu";
		mbox-names = "tx0", "tx1", "tx2", "tx3",
			     "rx0", "rx1", "rx2", "rx3",
			     "gip3";
		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
			  &lsio_mu1 3 3>;

		watchdog {
			compatible = "fsl,imx8qxp-sc-wdt", "fsl,imx-sc-wdt";
			timeout-sec = <60>;
		};
	};
};

serial@5a060000 {
	...
};