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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
commit | 2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch) | |
tree | 848558de17fb3008cdf4d861b01ac7781903ce39 /Documentation/driver-api/usb/typec.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream.tar.xz linux-upstream.zip |
Adding upstream version 6.1.76.upstream/6.1.76upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/driver-api/usb/typec.rst | 234 |
1 files changed, 234 insertions, 0 deletions
diff --git a/Documentation/driver-api/usb/typec.rst b/Documentation/driver-api/usb/typec.rst new file mode 100644 index 000000000..201163d8c --- /dev/null +++ b/Documentation/driver-api/usb/typec.rst @@ -0,0 +1,234 @@ +.. _typec: + +USB Type-C connector class +========================== + +Introduction +------------ + +The typec class is meant for describing the USB Type-C ports in a system to the +user space in unified fashion. The class is designed to provide nothing else +except the user space interface implementation in hope that it can be utilized +on as many platforms as possible. + +The platforms are expected to register every USB Type-C port they have with the +class. In a normal case the registration will be done by a USB Type-C or PD PHY +driver, but it may be a driver for firmware interface such as UCSI, driver for +USB PD controller or even driver for Thunderbolt3 controller. This document +considers the component registering the USB Type-C ports with the class as "port +driver". + +On top of showing the capabilities, the class also offer user space control over +the roles and alternate modes of ports, partners and cable plugs when the port +driver is capable of supporting those features. + +The class provides an API for the port drivers described in this document. The +attributes are described in Documentation/ABI/testing/sysfs-class-typec. + +User space interface +-------------------- +Every port will be presented as its own device under /sys/class/typec/. The +first port will be named "port0", the second "port1" and so on. + +When connected, the partner will be presented also as its own device under +/sys/class/typec/. The parent of the partner device will always be the port it +is attached to. The partner attached to port "port0" will be named +"port0-partner". Full path to the device would be +/sys/class/typec/port0/port0-partner/. + +The cable and the two plugs on it may also be optionally presented as their own +devices under /sys/class/typec/. The cable attached to the port "port0" port +will be named port0-cable and the plug on the SOP Prime end (see USB Power +Delivery Specification ch. 2.4) will be named "port0-plug0" and on the SOP +Double Prime end "port0-plug1". The parent of a cable will always be the port, +and the parent of the cable plugs will always be the cable. + +If the port, partner or cable plug supports Alternate Modes, every supported +Alternate Mode SVID will have their own device describing them. Note that the +Alternate Mode devices will not be attached to the typec class. The parent of an +alternate mode will be the device that supports it, so for example an alternate +mode of port0-partner will be presented under /sys/class/typec/port0-partner/. +Every mode that is supported will have its own group under the Alternate Mode +device named "mode<index>", for example /sys/class/typec/port0/<alternate +mode>/mode1/. The requests for entering/exiting a mode can be done with "active" +attribute file in that group. + +Driver API +---------- + +Registering the ports +~~~~~~~~~~~~~~~~~~~~~ + +The port drivers will describe every Type-C port they control with struct +typec_capability data structure, and register them with the following API: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_register_port typec_unregister_port + +When registering the ports, the prefer_role member in struct typec_capability +deserves special notice. If the port that is being registered does not have +initial role preference, which means the port does not execute Try.SNK or +Try.SRC by default, the member must have value TYPEC_NO_PREFERRED_ROLE. +Otherwise if the port executes Try.SNK by default, the member must have value +TYPEC_DEVICE, and with Try.SRC the value must be TYPEC_HOST. + +Registering Partners +~~~~~~~~~~~~~~~~~~~~ + +After successful connection of a partner, the port driver needs to register the +partner with the class. Details about the partner need to be described in struct +typec_partner_desc. The class copies the details of the partner during +registration. The class offers the following API for registering/unregistering +partners. + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_register_partner typec_unregister_partner + +The class will provide a handle to struct typec_partner if the registration was +successful, or NULL. + +If the partner is USB Power Delivery capable, and the port driver is able to +show the result of Discover Identity command, the partner descriptor structure +should include handle to struct usb_pd_identity instance. The class will then +create a sysfs directory for the identity under the partner device. The result +of Discover Identity command can then be reported with the following API: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_partner_set_identity + +Registering Cables +~~~~~~~~~~~~~~~~~~ + +After successful connection of a cable that supports USB Power Delivery +Structured VDM "Discover Identity", the port driver needs to register the cable +and one or two plugs, depending if there is CC Double Prime controller present +in the cable or not. So a cable capable of SOP Prime communication, but not SOP +Double Prime communication, should only have one plug registered. For more +information about SOP communication, please read chapter about it from the +latest USB Power Delivery specification. + +The plugs are represented as their own devices. The cable is registered first, +followed by registration of the cable plugs. The cable will be the parent device +for the plugs. Details about the cable need to be described in struct +typec_cable_desc and about a plug in struct typec_plug_desc. The class copies +the details during registration. The class offers the following API for +registering/unregistering cables and their plugs: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_register_cable typec_unregister_cable typec_register_plug typec_unregister_plug + +The class will provide a handle to struct typec_cable and struct typec_plug if +the registration is successful, or NULL if it isn't. + +If the cable is USB Power Delivery capable, and the port driver is able to show +the result of Discover Identity command, the cable descriptor structure should +include handle to struct usb_pd_identity instance. The class will then create a +sysfs directory for the identity under the cable device. The result of Discover +Identity command can then be reported with the following API: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_cable_set_identity + +Notifications +~~~~~~~~~~~~~ + +When the partner has executed a role change, or when the default roles change +during connection of a partner or cable, the port driver must use the following +APIs to report it to the class: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_set_data_role typec_set_pwr_role typec_set_vconn_role typec_set_pwr_opmode + +Alternate Modes +~~~~~~~~~~~~~~~ + +USB Type-C ports, partners and cable plugs may support Alternate Modes. Each +Alternate Mode will have identifier called SVID, which is either a Standard ID +given by USB-IF or vendor ID, and each supported SVID can have 1 - 6 modes. The +class provides struct typec_mode_desc for describing individual mode of a SVID, +and struct typec_altmode_desc which is a container for all the supported modes. + +Ports that support Alternate Modes need to register each SVID they support with +the following API: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_port_register_altmode + +If a partner or cable plug provides a list of SVIDs as response to USB Power +Delivery Structured VDM Discover SVIDs message, each SVID needs to be +registered. + +API for the partners: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_partner_register_altmode + +API for the Cable Plugs: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_plug_register_altmode + +So ports, partners and cable plugs will register the alternate modes with their +own functions, but the registration will always return a handle to struct +typec_altmode on success, or NULL. The unregistration will happen with the same +function: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_unregister_altmode + +If a partner or cable plug enters or exits a mode, the port driver needs to +notify the class with the following API: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_altmode_update_active + +Multiplexer/DeMultiplexer Switches +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +USB Type-C connectors may have one or more mux/demux switches behind them. Since +the plugs can be inserted right-side-up or upside-down, a switch is needed to +route the correct data pairs from the connector to the USB controllers. If +Alternate or Accessory Modes are supported, another switch is needed that can +route the pins on the connector to some other component besides USB. USB Type-C +Connector Class supplies an API for registering those switches. + +.. kernel-doc:: drivers/usb/typec/mux.c + :functions: typec_switch_register typec_switch_unregister typec_mux_register typec_mux_unregister + +In most cases the same physical mux will handle both the orientation and mode. +However, as the port drivers will be responsible for the orientation, and the +alternate mode drivers for the mode, the two are always separated into their +own logical components: "mux" for the mode and "switch" for the orientation. + +When a port is registered, USB Type-C Connector Class requests both the mux and +the switch for the port. The drivers can then use the following API for +controlling them: + +.. kernel-doc:: drivers/usb/typec/class.c + :functions: typec_set_orientation typec_set_mode + +If the connector is dual-role capable, there may also be a switch for the data +role. USB Type-C Connector Class does not supply separate API for them. The +port drivers can use USB Role Class API with those. + +Illustration of the muxes behind a connector that supports an alternate mode:: + + ------------------------ + | Connector | + ------------------------ + | | + ------------------------ + \ Orientation / + -------------------- + | + -------------------- + / Mode \ + ------------------------ + / \ + ------------------------ -------------------- + | Alt Mode | / USB Role \ + ------------------------ ------------------------ + / \ + ------------------------ ------------------------ + | USB Host | | USB Device | + ------------------------ ------------------------ |