cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
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intel-pmc-mux.rst (4861B)

      1.. SPDX-License-Identifier: GPL-2.0
      2
      3=====================
      4Intel North Mux-Agent
      5=====================
      6
      7Introduction
      8============
      9
     10North Mux-Agent is a function of the Intel PMC firmware that is supported on
     11most Intel based platforms that have the PMC microcontroller. It's used for
     12configuring the various USB Multiplexer/DeMultiplexers on the system. The
     13platforms that allow the mux-agent to be configured from the operating system
     14have an ACPI device object (node) with HID "INTC105C" that represents it.
     15
     16The North Mux-Agent (aka. Intel PMC Mux Control, or just mux-agent) driver
     17communicates with the PMC microcontroller by using the PMC IPC method
     18(drivers/platform/x86/intel_scu_ipc.c). The driver registers with the USB Type-C
     19Mux Class which allows the USB Type-C Controller and Interface drivers to
     20configure the cable plug orientation and mode (with Alternate Modes). The driver
     21also registers with the USB Role Class in order to support both USB Host and
     22Device modes. The driver is located here: drivers/usb/typec/mux/intel_pmc_mux.c.
     23
     24Port nodes
     25==========
     26
     27General
     28-------
     29
     30For every USB Type-C connector under the mux-agent control on the system, there
     31is a separate child node under the PMC mux-agent device node. Those nodes do not
     32represent the actual connectors, but instead the "channels" in the mux-agent
     33that are associated with the connectors::
     34
     35	Scope (_SB.PCI0.PMC.MUX)
     36	{
     37	    Device (CH0)
     38	    {
     39		Name (_ADR, 0)
     40	    }
     41
     42	    Device (CH1)
     43	    {
     44		Name (_ADR, 1)
     45	    }
     46	}
     47
     48_PLD (Physical Location of Device)
     49----------------------------------
     50
     51The optional _PLD object can be used with the port (the channel) nodes. If _PLD
     52is supplied, it should match the connector node _PLD::
     53
     54	Scope (_SB.PCI0.PMC.MUX)
     55	{
     56	    Device (CH0)
     57	    {
     58		Name (_ADR, 0)
     59	        Method (_PLD, 0, NotSerialized)
     60                {
     61		    /* Consider this as pseudocode. */
     62		    Return (\_SB.USBC.CON0._PLD())
     63		}
     64	    }
     65	}
     66
     67Mux-agent specific _DSD Device Properties
     68-----------------------------------------
     69
     70Port Numbers
     71~~~~~~~~~~~~
     72
     73In order to configure the muxes behind a USB Type-C connector, the PMC firmware
     74needs to know the USB2 port and the USB3 port that is associated with the
     75connector. The driver extracts the correct port numbers by reading specific _DSD
     76device properties named "usb2-port-number" and "usb3-port-number". These
     77properties have integer value that means the port index. The port index number
     78is 1's based, and value 0 is illegal. The driver uses the numbers extracted from
     79these device properties as-is when sending the mux-agent specific messages to
     80the PMC::
     81
     82	Name (_DSD, Package () {
     83	    ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
     84	    Package() {
     85	        Package () {"usb2-port-number", 6},
     86	        Package () {"usb3-port-number", 3},
     87	    },
     88	})
     89
     90Orientation
     91~~~~~~~~~~~
     92
     93Depending on the platform, the data and SBU lines coming from the connector may
     94be "fixed" from the mux-agent's point of view, which means the mux-agent driver
     95should not configure them according to the cable plug orientation. This can
     96happen for example if a retimer on the platform handles the cable plug
     97orientation. The driver uses a specific device properties "sbu-orientation"
     98(SBU) and "hsl-orientation" (data) to know if those lines are "fixed", and to
     99which orientation. The value that these properties have is a string value, and
    100it can be one that is defined for the USB Type-C connector orientation: "normal"
    101or "reversed"::
    102
    103	Name (_DSD, Package () {
    104	    ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
    105	    Package() {
    106	        Package () {"sbu-orientation", "normal"},
    107	        Package () {"hsl-orientation", "normal"},
    108	    },
    109	})
    110
    111Example ASL
    112===========
    113
    114The following ASL is an example that shows the mux-agent node, and two
    115connectors under its control::
    116
    117	Scope (_SB.PCI0.PMC)
    118	{
    119	    Device (MUX)
    120	    {
    121	        Name (_HID, "INTC105C")
    122
    123	        Device (CH0)
    124	        {
    125	            Name (_ADR, 0)
    126
    127	            Name (_DSD, Package () {
    128	                ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
    129	                Package() {
    130	                    Package () {"usb2-port-number", 6},
    131	                    Package () {"usb3-port-number", 3},
    132	                    Package () {"sbu-orientation", "normal"},
    133	                    Package () {"hsl-orientation", "normal"},
    134	                },
    135	            })
    136	        }
    137
    138	        Device (CH1)
    139	        {
    140	            Name (_ADR, 1)
    141
    142	            Name (_DSD, Package () {
    143	                ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
    144	                Package() {
    145	                    Package () {"usb2-port-number", 5},
    146	                    Package () {"usb3-port-number", 2},
    147	                    Package () {"sbu-orientation", "normal"},
    148	                    Package () {"hsl-orientation", "normal"},
    149	                },
    150	            })
    151	        }
    152	    }
    153	}