.. _typec:
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USB Type-C connector class
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==========================
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Introduction
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------------
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The typec class is meant for describing the USB Type-C ports in a system to the
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user space in unified fashion. The class is designed to provide nothing else
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except the user space interface implementation in hope that it can be utilized
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on as many platforms as possible.
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The platforms are expected to register every USB Type-C port they have with the
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class. In a normal case the registration will be done by a USB Type-C or PD PHY
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driver, but it may be a driver for firmware interface such as UCSI, driver for
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USB PD controller or even driver for Thunderbolt3 controller. This document
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considers the component registering the USB Type-C ports with the class as "port
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driver".
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On top of showing the capabilities, the class also offer user space control over
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the roles and alternate modes of ports, partners and cable plugs when the port
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driver is capable of supporting those features.
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The class provides an API for the port drivers described in this document. The
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attributes are described in Documentation/ABI/testing/sysfs-class-typec.
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User space interface
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--------------------
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Every port will be presented as its own device under /sys/class/typec/. The
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first port will be named "port0", the second "port1" and so on.
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When connected, the partner will be presented also as its own device under
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/sys/class/typec/. The parent of the partner device will always be the port it
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is attached to. The partner attached to port "port0" will be named
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"port0-partner". Full path to the device would be
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/sys/class/typec/port0/port0-partner/.
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The cable and the two plugs on it may also be optionally presented as their own
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devices under /sys/class/typec/. The cable attached to the port "port0" port
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will be named port0-cable and the plug on the SOP Prime end (see USB Power
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Delivery Specification ch. 2.4) will be named "port0-plug0" and on the SOP
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Double Prime end "port0-plug1". The parent of a cable will always be the port,
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and the parent of the cable plugs will always be the cable.
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If the port, partner or cable plug supports Alternate Modes, every supported
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Alternate Mode SVID will have their own device describing them. Note that the
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Alternate Mode devices will not be attached to the typec class. The parent of an
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alternate mode will be the device that supports it, so for example an alternate
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mode of port0-partner will be presented under /sys/class/typec/port0-partner/.
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Every mode that is supported will have its own group under the Alternate Mode
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device named "mode<index>", for example /sys/class/typec/port0/<alternate
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mode>/mode1/. The requests for entering/exiting a mode can be done with "active"
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attribute file in that group.
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Driver API
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----------
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Registering the ports
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~~~~~~~~~~~~~~~~~~~~~
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The port drivers will describe every Type-C port they control with struct
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typec_capability data structure, and register them with the following API:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_register_port typec_unregister_port
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When registering the ports, the prefer_role member in struct typec_capability
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deserves special notice. If the port that is being registered does not have
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initial role preference, which means the port does not execute Try.SNK or
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Try.SRC by default, the member must have value TYPEC_NO_PREFERRED_ROLE.
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Otherwise if the port executes Try.SNK by default, the member must have value
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TYPEC_DEVICE, and with Try.SRC the value must be TYPEC_HOST.
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Registering Partners
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~~~~~~~~~~~~~~~~~~~~
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After successful connection of a partner, the port driver needs to register the
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partner with the class. Details about the partner need to be described in struct
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typec_partner_desc. The class copies the details of the partner during
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registration. The class offers the following API for registering/unregistering
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partners.
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_register_partner typec_unregister_partner
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The class will provide a handle to struct typec_partner if the registration was
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successful, or NULL.
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If the partner is USB Power Delivery capable, and the port driver is able to
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show the result of Discover Identity command, the partner descriptor structure
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should include handle to struct usb_pd_identity instance. The class will then
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create a sysfs directory for the identity under the partner device. The result
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of Discover Identity command can then be reported with the following API:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_partner_set_identity
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Registering Cables
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~~~~~~~~~~~~~~~~~~
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After successful connection of a cable that supports USB Power Delivery
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Structured VDM "Discover Identity", the port driver needs to register the cable
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and one or two plugs, depending if there is CC Double Prime controller present
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in the cable or not. So a cable capable of SOP Prime communication, but not SOP
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Double Prime communication, should only have one plug registered. For more
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information about SOP communication, please read chapter about it from the
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latest USB Power Delivery specification.
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The plugs are represented as their own devices. The cable is registered first,
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followed by registration of the cable plugs. The cable will be the parent device
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for the plugs. Details about the cable need to be described in struct
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typec_cable_desc and about a plug in struct typec_plug_desc. The class copies
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the details during registration. The class offers the following API for
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registering/unregistering cables and their plugs:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_register_cable typec_unregister_cable typec_register_plug typec_unregister_plug
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The class will provide a handle to struct typec_cable and struct typec_plug if
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the registration is successful, or NULL if it isn't.
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If the cable is USB Power Delivery capable, and the port driver is able to show
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the result of Discover Identity command, the cable descriptor structure should
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include handle to struct usb_pd_identity instance. The class will then create a
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sysfs directory for the identity under the cable device. The result of Discover
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Identity command can then be reported with the following API:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_cable_set_identity
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Notifications
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~~~~~~~~~~~~~
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When the partner has executed a role change, or when the default roles change
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during connection of a partner or cable, the port driver must use the following
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APIs to report it to the class:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_set_data_role typec_set_pwr_role typec_set_vconn_role typec_set_pwr_opmode
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Alternate Modes
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~~~~~~~~~~~~~~~
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USB Type-C ports, partners and cable plugs may support Alternate Modes. Each
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Alternate Mode will have identifier called SVID, which is either a Standard ID
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given by USB-IF or vendor ID, and each supported SVID can have 1 - 6 modes. The
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class provides struct typec_mode_desc for describing individual mode of a SVID,
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and struct typec_altmode_desc which is a container for all the supported modes.
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Ports that support Alternate Modes need to register each SVID they support with
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the following API:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_port_register_altmode
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If a partner or cable plug provides a list of SVIDs as response to USB Power
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Delivery Structured VDM Discover SVIDs message, each SVID needs to be
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registered.
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API for the partners:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_partner_register_altmode
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API for the Cable Plugs:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_plug_register_altmode
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So ports, partners and cable plugs will register the alternate modes with their
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own functions, but the registration will always return a handle to struct
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typec_altmode on success, or NULL. The unregistration will happen with the same
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function:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_unregister_altmode
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If a partner or cable plug enters or exits a mode, the port driver needs to
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notify the class with the following API:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_altmode_update_active
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Multiplexer/DeMultiplexer Switches
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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USB Type-C connectors may have one or more mux/demux switches behind them. Since
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the plugs can be inserted right-side-up or upside-down, a switch is needed to
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route the correct data pairs from the connector to the USB controllers. If
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Alternate or Accessory Modes are supported, another switch is needed that can
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route the pins on the connector to some other component besides USB. USB Type-C
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Connector Class supplies an API for registering those switches.
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.. kernel-doc:: drivers/usb/typec/mux.c
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:functions: typec_switch_register typec_switch_unregister typec_mux_register typec_mux_unregister
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In most cases the same physical mux will handle both the orientation and mode.
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However, as the port drivers will be responsible for the orientation, and the
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alternate mode drivers for the mode, the two are always separated into their
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own logical components: "mux" for the mode and "switch" for the orientation.
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When a port is registered, USB Type-C Connector Class requests both the mux and
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the switch for the port. The drivers can then use the following API for
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controlling them:
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.. kernel-doc:: drivers/usb/typec/class.c
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:functions: typec_set_orientation typec_set_mode
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If the connector is dual-role capable, there may also be a switch for the data
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role. USB Type-C Connector Class does not supply separate API for them. The
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port drivers can use USB Role Class API with those.
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Illustration of the muxes behind a connector that supports an alternate mode::
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------------------------
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| Connector |
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------------------------
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| |
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------------------------
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\ Orientation /
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--------------------
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--------------------
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/ Mode \
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------------------------
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/ \
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------------------------ --------------------
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| Alt Mode | / USB Role \
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------------------------ ------------------------
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/ \
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------------------------ ------------------------
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| USB Host | | USB Device |
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------------------------ ------------------------
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