path: root/Documentation/driver-api
diff options
Diffstat (limited to 'Documentation/driver-api')
9 files changed, 250 insertions, 13 deletions
diff --git a/Documentation/driver-api/gpio/driver.rst b/Documentation/driver-api/gpio/driver.rst
index a6c14ff0c54f..a92d8837b62b 100644
--- a/Documentation/driver-api/gpio/driver.rst
+++ b/Documentation/driver-api/gpio/driver.rst
@@ -434,7 +434,9 @@ try_module_get()). A GPIO driver can use the following functions instead
to request and free descriptors without being pinned to the kernel forever::
struct gpio_desc *gpiochip_request_own_desc(struct gpio_desc *desc,
- const char *label)
+ u16 hwnum,
+ const char *label,
+ enum gpiod_flags flags)
void gpiochip_free_own_desc(struct gpio_desc *desc)
diff --git a/Documentation/driver-api/i3c/device-driver-api.rst b/Documentation/driver-api/i3c/device-driver-api.rst
new file mode 100644
index 000000000000..85bc3381cd3e
--- /dev/null
+++ b/Documentation/driver-api/i3c/device-driver-api.rst
@@ -0,0 +1,9 @@
+.. SPDX-License-Identifier: GPL-2.0
+I3C device driver API
+.. kernel-doc:: include/linux/i3c/device.h
+.. kernel-doc:: drivers/i3c/device.c
diff --git a/Documentation/driver-api/i3c/index.rst b/Documentation/driver-api/i3c/index.rst
new file mode 100644
index 000000000000..783d6dad054b
--- /dev/null
+++ b/Documentation/driver-api/i3c/index.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: GPL-2.0
+I3C subsystem
+.. toctree::
+ protocol
+ device-driver-api
+ master-driver-api
diff --git a/Documentation/driver-api/i3c/master-driver-api.rst b/Documentation/driver-api/i3c/master-driver-api.rst
new file mode 100644
index 000000000000..332552b28358
--- /dev/null
+++ b/Documentation/driver-api/i3c/master-driver-api.rst
@@ -0,0 +1,9 @@
+.. SPDX-License-Identifier: GPL-2.0
+I3C master controller driver API
+.. kernel-doc:: drivers/i3c/master.c
+.. kernel-doc:: include/linux/i3c/master.h
diff --git a/Documentation/driver-api/i3c/protocol.rst b/Documentation/driver-api/i3c/protocol.rst
new file mode 100644
index 000000000000..dae3b6d32c6b
--- /dev/null
+++ b/Documentation/driver-api/i3c/protocol.rst
@@ -0,0 +1,203 @@
+.. SPDX-License-Identifier: GPL-2.0
+I3C protocol
+This chapter will focus on aspects that matter to software developers. For
+everything hardware related (like how things are transmitted on the bus, how
+collisions are prevented, ...) please have a look at the I3C specification.
+This document is just a brief introduction to the I3C protocol and the concepts
+it brings to the table. If you need more information, please refer to the MIPI
+I3C specification (can be downloaded here
+The I3C (pronounced 'eye-three-see') is a MIPI standardized protocol designed
+to overcome I2C limitations (limited speed, external signals needed for
+interrupts, no automatic detection of the devices connected to the bus, ...)
+while remaining power-efficient.
+I3C Bus
+An I3C bus is made of several I3C devices and possibly some I2C devices as
+well, but let's focus on I3C devices for now.
+An I3C device on the I3C bus can have one of the following roles:
+* Master: the device is driving the bus. It's the one in charge of initiating
+ transactions or deciding who is allowed to talk on the bus (slave generated
+ events are possible in I3C, see below).
+* Slave: the device acts as a slave, and is not able to send frames to another
+ slave on the bus. The device can still send events to the master on
+ its own initiative if the master allowed it.
+I3C is a multi-master protocol, so there might be several masters on a bus,
+though only one device can act as a master at a given time. In order to gain
+bus ownership, a master has to follow a specific procedure.
+Each device on the I3C bus has to be assigned a dynamic address to be able to
+communicate. Until this is done, the device should only respond to a limited
+set of commands. If it has a static address (also called legacy I2C address),
+the device can reply to I2C transfers.
+In addition to these per-device addresses, the protocol defines a broadcast
+address in order to address all devices on the bus.
+Once a dynamic address has been assigned to a device, this address will be used
+for any direct communication with the device. Note that even after being
+assigned a dynamic address, the device should still process broadcast messages.
+I3C Device discovery
+The I3C protocol defines a mechanism to automatically discover devices present
+on the bus, their capabilities and the functionalities they provide. In this
+regard I3C is closer to a discoverable bus like USB than it is to I2C or SPI.
+The discovery mechanism is called DAA (Dynamic Address Assignment), because it
+not only discovers devices but also assigns them a dynamic address.
+During DAA, each I3C device reports 3 important things:
+* BCR: Bus Characteristic Register. This 8-bit register describes the device bus
+ related capabilities
+* DCR: Device Characteristic Register. This 8-bit register describes the
+ functionalities provided by the device
+* Provisional ID: A 48-bit unique identifier. On a given bus there should be no
+ Provisional ID collision, otherwise the discovery mechanism may fail.
+I3C slave events
+The I3C protocol allows slaves to generate events on their own, and thus allows
+them to take temporary control of the bus.
+This mechanism is called IBI for In Band Interrupts, and as stated in the name,
+it allows devices to generate interrupts without requiring an external signal.
+During DAA, each device on the bus has been assigned an address, and this
+address will serve as a priority identifier to determine who wins if 2 different
+devices are generating an interrupt at the same moment on the bus (the lower the
+dynamic address the higher the priority).
+Masters are allowed to inhibit interrupts if they want to. This inhibition
+request can be broadcast (applies to all devices) or sent to a specific
+I3C Hot-Join
+The Hot-Join mechanism is similar to USB hotplug. This mechanism allows
+slaves to join the bus after it has been initialized by the master.
+This covers the following use cases:
+* the device is not powered when the bus is probed
+* the device is hotplugged on the bus through an extension board
+This mechanism is relying on slave events to inform the master that a new
+device joined the bus and is waiting for a dynamic address.
+The master is then free to address the request as it wishes: ignore it or
+assign a dynamic address to the slave.
+I3C transfer types
+If you omit SMBus (which is just a standardization on how to access registers
+exposed by I2C devices), I2C has only one transfer type.
+I3C defines 3 different classes of transfer in addition to I2C transfers which
+are here for backward compatibility with I2C devices.
+I3C CCC commands
+CCC (Common Command Code) commands are meant to be used for anything that is
+related to bus management and all features that are common to a set of devices.
+CCC commands contain an 8-bit CCC ID describing the command that is executed.
+The MSB of this ID specifies whether this is a broadcast command (bit7 = 0) or a
+unicast one (bit7 = 1).
+The command ID can be followed by a payload. Depending on the command, this
+payload is either sent by the master sending the command (write CCC command),
+or sent by the slave receiving the command (read CCC command). Of course, read
+accesses only apply to unicast commands.
+Note that, when sending a CCC command to a specific device, the device address
+is passed in the first byte of the payload.
+The payload length is not explicitly passed on the bus, and should be extracted
+from the CCC ID.
+Note that vendors can use a dedicated range of CCC IDs for their own commands
+(0x61-0x7f and 0xe0-0xef).
+I3C Private SDR transfers
+Private SDR (Single Data Rate) transfers should be used for anything that is
+device specific and does not require high transfer speed.
+It is the equivalent of I2C transfers but in the I3C world. Each transfer is
+passed the device address (dynamic address assigned during DAA), a payload
+and a direction.
+The only difference with I2C is that the transfer is much faster (typical clock
+frequency is 12.5MHz).
+I3C HDR commands
+HDR commands should be used for anything that is device specific and requires
+high transfer speed.
+The first thing attached to an HDR command is the HDR mode. There are currently
+3 different modes defined by the I3C specification (refer to the specification
+for more details):
+* HDR-DDR: Double Data Rate mode
+* HDR-TSP: Ternary Symbol Pure. Only usable on busses with no I2C devices
+* HDR-TSL: Ternary Symbol Legacy. Usable on busses with I2C devices
+When sending an HDR command, the whole bus has to enter HDR mode, which is done
+using a broadcast CCC command.
+Once the bus has entered a specific HDR mode, the master sends the HDR command.
+An HDR command is made of:
+* one 16-bits command word in big endian
+* N 16-bits data words in big endian
+Those words may be wrapped with specific preambles/post-ambles which depend on
+the chosen HDR mode and are detailed here (see the specification for more
+The 16-bits command word is made of:
+* bit[15]: direction bit, read is 1, write is 0
+* bit[14:8]: command code. Identifies the command being executed, the amount of
+ data words and their meaning
+* bit[7:1]: I3C address of the device this command is addressed to
+* bit[0]: reserved/parity-bit
+Backward compatibility with I2C devices
+The I3C protocol has been designed to be backward compatible with I2C devices.
+This backward compatibility allows one to connect a mix of I2C and I3C devices
+on the same bus, though, in order to be really efficient, I2C devices should
+be equipped with 50 ns spike filters.
+I2C devices can't be discovered like I3C ones and have to be statically
+declared. In order to let the master know what these devices are capable of
+(both in terms of bus related limitations and functionalities), the software
+has to provide some information, which is done through the LVR (Legacy I2C
+Virtual Register).
diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst
index 909f991b4c0d..ab38ced66a44 100644
--- a/Documentation/driver-api/index.rst
+++ b/Documentation/driver-api/index.rst
@@ -33,6 +33,7 @@ available subsections can be seen below.
+ i3c/index
diff --git a/Documentation/driver-api/usb/index.rst b/Documentation/driver-api/usb/index.rst
index 8fe995a1ec94..cfa8797ea614 100644
--- a/Documentation/driver-api/usb/index.rst
+++ b/Documentation/driver-api/usb/index.rst
@@ -19,6 +19,7 @@ Linux USB API
+ typec_bus
.. only:: subproject and html
diff --git a/Documentation/driver-api/usb/typec.rst b/Documentation/driver-api/usb/typec.rst
index 48ff58095f11..201163d8c13e 100644
--- a/Documentation/driver-api/usb/typec.rst
+++ b/Documentation/driver-api/usb/typec.rst
@@ -1,3 +1,4 @@
+.. _typec:
USB Type-C connector class
diff --git a/Documentation/driver-api/usb/typec_bus.rst b/Documentation/driver-api/usb/typec_bus.rst
index d5eec1715b5b..f47a69bff498 100644
--- a/Documentation/driver-api/usb/typec_bus.rst
+++ b/Documentation/driver-api/usb/typec_bus.rst
@@ -13,10 +13,10 @@ every alternate mode, so every alternate mode will need a custom driver.
USB Type-C bus allows binding a driver to the discovered partner alternate
modes by using the SVID and the mode number.
-USB Type-C Connector Class provides a device for every alternate mode a port
-supports, and separate device for every alternate mode the partner supports.
-The drivers for the alternate modes are bound to the partner alternate mode
-devices, and the port alternate mode devices must be handled by the port
+:ref:`USB Type-C Connector Class <typec>` provides a device for every alternate
+mode a port supports, and separate device for every alternate mode the partner
+supports. The drivers for the alternate modes are bound to the partner alternate
+mode devices, and the port alternate mode devices must be handled by the port
When a new partner alternate mode device is registered, it is linked to the
@@ -46,7 +46,7 @@ enter any modes on their own.
``->vdm`` is the most important callback in the operation callbacks vector. It
will be used to deliver all the SVID specific commands from the partner to the
alternate mode driver, and vice versa in case of port drivers. The drivers send
-the SVID specific commands to each other using :c:func:`typec_altmode_vmd()`.
+the SVID specific commands to each other using :c:func:`typec_altmode_vdm()`.
If the communication with the partner using the SVID specific commands results
in need to reconfigure the pins on the connector, the alternate mode driver
@@ -67,15 +67,15 @@ Type-C Specification, and also put the connector back to ``TYPEC_STATE_USB``
after the mode has been exited.
An example of working definitions for SVID specific pin configurations would
-look like this:
+look like this::
-enum {
- ...
+ enum {
+ ...
+ };
-Helper macro ``TYPEC_MODAL_STATE()`` can also be used:
+Helper macro ``TYPEC_MODAL_STATE()`` can also be used::