xref: /kernel/linux/linux-5.10/Documentation/firmware-guide/acpi/intel-pmc-mux.rst

.. SPDX-License-Identifier: GPL-2.0

=====================
Intel North Mux-Agent
=====================

Introduction
============

North Mux-Agent is a function of the Intel PMC firmware that is supported on
most Intel based platforms that have the PMC microcontroller. It's used for
configuring the various USB Multiplexer/DeMultiplexers on the system. The
platforms that allow the mux-agent to be configured from the operating system
have an ACPI device object (node) with HID "INTC105C" that represents it.

The North Mux-Agent (aka. Intel PMC Mux Control, or just mux-agent) driver
communicates with the PMC microcontroller by using the PMC IPC method
(drivers/platform/x86/intel_scu_ipc.c). The driver registers with the USB Type-C
Mux Class which allows the USB Type-C Controller and Interface drivers to
configure the cable plug orientation and mode (with Alternate Modes). The driver
also registers with the USB Role Class in order to support both USB Host and
Device modes. The driver is located here: drivers/usb/typec/mux/intel_pmc_mux.c.

Port nodes
==========

General
-------

For every USB Type-C connector under the mux-agent control on the system, there
is a separate child node under the PMC mux-agent device node. Those nodes do not
represent the actual connectors, but instead the "channels" in the mux-agent
that are associated with the connectors::

	Scope (_SB.PCI0.PMC.MUX)
	{
	    Device (CH0)
	    {
		Name (_ADR, 0)
	    }

	    Device (CH1)
	    {
		Name (_ADR, 1)
	    }
	}

_PLD (Physical Location of Device)
----------------------------------

The optional _PLD object can be used with the port (the channel) nodes. If _PLD
is supplied, it should match the connector node _PLD::

	Scope (_SB.PCI0.PMC.MUX)
	{
	    Device (CH0)
	    {
		Name (_ADR, 0)
	        Method (_PLD, 0, NotSerialized)
                {
		    /* Consider this as pseudocode. */
		    Return (\_SB.USBC.CON0._PLD())
		}
	    }
	}

Mux-agent specific _DSD Device Properties
-----------------------------------------

Port Numbers
~~~~~~~~~~~~

In order to configure the muxes behind a USB Type-C connector, the PMC firmware
needs to know the USB2 port and the USB3 port that is associated with the
connector. The driver extracts the correct port numbers by reading specific _DSD
device properties named "usb2-port-number" and "usb3-port-number". These
properties have integer value that means the port index. The port index number
is 1's based, and value 0 is illegal. The driver uses the numbers extracted from
these device properties as-is when sending the mux-agent specific messages to
the PMC::

	Name (_DSD, Package () {
	    ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
	    Package() {
	        Package () {"usb2-port-number", 6},
	        Package () {"usb3-port-number", 3},
	    },
	})

Orientation
~~~~~~~~~~~

Depending on the platform, the data and SBU lines coming from the connector may
be "fixed" from the mux-agent's point of view, which means the mux-agent driver
should not configure them according to the cable plug orientation. This can
happen for example if a retimer on the platform handles the cable plug
orientation. The driver uses a specific device properties "sbu-orientation"
(SBU) and "hsl-orientation" (data) to know if those lines are "fixed", and to
which orientation. The value that these properties have is a string value, and
it can be one that is defined for the USB Type-C connector orientation: "normal"
or "reversed"::

	Name (_DSD, Package () {
	    ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
	    Package() {
	        Package () {"sbu-orientation", "normal"},
	        Package () {"hsl-orientation", "normal"},
	    },
	})

Example ASL
===========

The following ASL is an example that shows the mux-agent node, and two
connectors under its control::

	Scope (_SB.PCI0.PMC)
	{
	    Device (MUX)
	    {
	        Name (_HID, "INTC105C")

	        Device (CH0)
	        {
	            Name (_ADR, 0)

	            Name (_DSD, Package () {
	                ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
	                Package() {
	                    Package () {"usb2-port-number", 6},
	                    Package () {"usb3-port-number", 3},
	                    Package () {"sbu-orientation", "normal"},
	                    Package () {"hsl-orientation", "normal"},
	                },
	            })
	        }

	        Device (CH1)
	        {
	            Name (_ADR, 1)

	            Name (_DSD, Package () {
	                ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
	                Package() {
	                    Package () {"usb2-port-number", 5},
	                    Package () {"usb3-port-number", 2},
	                    Package () {"sbu-orientation", "normal"},
	                    Package () {"hsl-orientation", "normal"},
	                },
	            })
	        }
	    }
	}