Adding documentation that describes how the PMC mux-agent
function is described in the ACPI tables.
Signed-off-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
---
.../firmware-guide/acpi/intel-pmc-mux.rst | 153 ++++++++++++++++++
1 file changed, 153 insertions(+)
create mode 100644 Documentation/firmware-guide/acpi/intel-pmc-mux.rst
diff --git a/Documentation/firmware-guide/acpi/intel-pmc-mux.rst b/Documentation/firmware-guide/acpi/intel-pmc-mux.rst
new file mode 100644
index 000000000000..99b86710f02b
--- /dev/null
+++ b/Documentation/firmware-guide/acpi/intel-pmc-mux.rst
@@ -0,0 +1,153 @@
+.. 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"},
+ },
+ })
+ }
+ }
+ }
--
2.26.2
