[v3,3/8] Documentation: i3c: Add I3C target mode controller and function

diff --git a/Documentation/driver-api/i3c/index.rst b/Documentation/driver-api/i3c/index.rst
index 783d6dad054b6..345a43c9f61b0 100644
--- a/Documentation/driver-api/i3c/index.rst
+++ b/Documentation/driver-api/i3c/index.rst
@@ -9,3 +9,4 @@  I3C subsystem
    protocol
    device-driver-api
    master-driver-api
+   target/index
diff --git a/Documentation/driver-api/i3c/target/i3c-target-cfs.rst b/Documentation/driver-api/i3c/target/i3c-target-cfs.rst
new file mode 100644
index 0000000000000..1fcf829dc4ae2
--- /dev/null
+++ b/Documentation/driver-api/i3c/target/i3c-target-cfs.rst
@@ -0,0 +1,109 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+=======================================
+Configuring I3C Target Using CONFIGFS
+=======================================
+
+:Author: Frank Li <Frank.Li@nxp.com>
+
+The I3C Target Core exposes configfs entry (i3c_target) to configure the I3C
+target function and to bind the target function with the target controller.
+(For introducing other mechanisms to configure the I3C Target Function refer to
+[1]).
+
+Mounting configfs
+=================
+
+The I3C Target Core layer creates i3c_target directory in the mounted configfs
+directory. configfs can be mounted using the following command::
+
+	mount -t configfs none /sys/kernel/config
+
+Directory Structure
+===================
+
+The i3c_target configfs has two directories at its root: controllers and
+functions. Every Controller device present in the system will have an entry in
+the *controllers* directory and every Function driver present in the system will
+have an entry in the *functions* directory.
+::
+
+	/sys/kernel/config/i3c_target/
+		.. controllers/
+		.. functions/
+
+Creating Function Device
+===================
+
+Every registered Function driver will be listed in controllers directory. The
+entries corresponding to Function driver will be created by the Function core.
+::
+
+	/sys/kernel/config/i3c_target/functions/
+		.. <Function Driver1>/
+			... <Function Device 11>/
+			... <Function Device 21>/
+			... <Function Device 31>/
+		.. <Function Driver2>/
+			... <Function Device 12>/
+			... <Function Device 22>/
+
+In order to create a <Function device> of the type probed by <Function Driver>,
+the user has to create a directory inside <Function DriverN>.
+
+Every <Function device> directory consists of the following entries that can be
+used to configure the standard configuration header of the target function.
+(These entries are created by the framework when any new <Function Device> is
+created)
+::
+
+		.. <Function Driver1>/
+			... <Function Device 11>/
+				... vendor_id
+				... part_id
+				... bcr
+				... dcr
+				... ext_id
+				... instance_id
+				... max_read_len
+				... max_write_len
+				... vendor_info
+
+Controller Device
+==========
+
+Every registered Controller device will be listed in controllers directory. The
+entries corresponding to Controller device will be created by the Controller
+core.
+::
+
+	/sys/kernel/config/i3c_target/controllers/
+		.. <Controller Device1>/
+			... <Symlink Function Device11>/
+		.. <Controller Device2>/
+			... <Symlink Function Device21>/
+
+The <Controller Device> directory will have a list of symbolic links to
+<Function Device>. These symbolic links should be created by the user to
+represent the functions present in the target device. Only <Function Device>
+that represents a physical function can be linked to a Controller device.
+
+::
+
+			 | controllers/
+				| <Directory: Controller name>/
+					| <Symbolic Link: Function>
+			 | functions/
+				| <Directory: Function driver>/
+					| <Directory: Function device>/
+						| vendor_id
+						| part_id
+						| bcr
+						| dcr
+						| ext_id
+						| instance_id
+						| max_read_len
+						| max_write_len
+						| vendor_info
+
+[1] Documentation/I3C/target/pci-target.rst
diff --git a/Documentation/driver-api/i3c/target/i3c-target.rst b/Documentation/driver-api/i3c/target/i3c-target.rst
new file mode 100644
index 0000000000000..09ae26b1f311a
--- /dev/null
+++ b/Documentation/driver-api/i3c/target/i3c-target.rst
@@ -0,0 +1,189 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+:Author: Frank Li <Frank.Li@nxp.com>
+
+This document is a guide to use the I3C Target Framework in order to create
+target controller driver, target function driver, and using configfs interface
+to bind the function driver to the controller driver.
+
+Introduction
+============
+
+Linux has a comprehensive I3C subsystem to support I3C controllers that
+operates in master mode. The subsystem has capability to scan I3C bus,assign
+i3c device address, load I3C driver (based on Manufacturer ID, part ID),
+support other services like hot-join, In-Band Interrupt(IBI).
+
+However the I3C controller IP integrated in some SoCs is capable of operating
+either in Master mode or Target mode. I3C Target Framework will add target mode
+support in Linux. This will help to run Linux in an target system which can
+have a wide variety of use cases from testing or validation, co-processor
+accelerator, etc.
+
+I3C Target Core
+=================
+
+The I3C Target Core layer comprises 3 components: the Target Controller
+library, the Target Function library, and the configfs layer to bind the target
+function with the target controller.
+
+I3C Target Controller Library
+------------------------------------
+
+The Controller library provides APIs to be used by the controller that can
+operate in target mode. It also provides APIs to be used by function
+driver/library in order to implement a particular target function.
+
+APIs for the I3C Target controller Driver
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This section lists the APIs that the I3C Target core provides to be used by the
+I3C controller driver.
+
+* devm_i3c_target_ctrl_create()/i3c_target_ctrl_create()
+
+   The I3C controller driver should implement the following ops:
+
+	* set_config: ops to set i3c configuration
+	* enable: ops to enable controller
+	* disable: ops to disable controller
+	* raise_ibi: ops to raise IBI to master controller
+	* alloc_request: ops to alloc a transfer request
+	* free_request: ops to free a transfer request
+	* queue: ops to queue a request to transfer queue
+	* dequeue: ops to dequeue a request from transfer queue
+	* cancel_all_reqs: ops to cancel all request from transfer queue
+        * fifo_status: ops to get fifo status
+        * fifo_flush: ops to flush hardware fifo
+	* get_features: ops to get controller supported features
+
+   The I3C controller driver can then create a new Controller device by
+   invoking devm_i3c_target_ctrl_create()/i3c_target_ctrl_create().
+
+* devm_i3c_target_ctrl_destroy()/i3c_target_ctrl_destroy()
+
+   The I3C controller driver can destroy the Controller device created by
+   either devm_i3c_target_ctrl_create() or i3c_target_ctrl_create() using
+   devm_i3c_target_ctrl_destroy() or i3c_target_ctrl_destroy().
+
+I3C Target Controller APIs for the I3C Target Function Driver
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This section lists the APIs that the I3C Target core provides to be used by the
+I3C target function driver.
+
+* i3c_target_ctrl_set_config()
+
+   The I3C target function driver should use i3c_target_ctrl_set_config() to
+   write i3c configuration to the target controller.
+
+* i3c_target_ctrl_enable()/i3c_target_ctrl_disable()
+
+   The I3C target function driver should use i3c_target_ctrl_enable()/
+   i3c_target_ctrl_disable() to enable/disable i3c target controller.
+
+* i3c_target_ctrl_alloc_request()/i3c_target_ctrl_free_request()
+
+   The I3C target function driver should usei3c_target_ctrl_alloc_request() /
+   i3c_target_ctrl_free_request() to alloc/free a i3c request.
+
+* i3c_target_ctrl_raise_ibi()
+
+   The I3C target function driver should use i3c_target_ctrl_raise_ibi() to
+   raise IBI.
+
+* i3c_target_ctrl_queue()/i3c_target_ctrl_dequeue()
+
+   The I3C target function driver should use i3c_target_ctrl_queue()/
+   i3c_target_ctrl_dequeue(), to queue/dequeue I3C transfer to/from transfer
+   queue.
+
+* i3c_target_ctrl_get_features()
+
+   The I3C target function driver should use i3c_target_ctrl_get_features() to
+   get I3C target controller supported features.
+
+Other I3C Target Controller APIs
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are other APIs provided by the Controller library. These are used for
+binding the I3C Target Function device with Controlller device. i3c-cfs.c can
+be used as reference for using these APIs.
+
+* i3c_target_ctrl_get()
+
+   Get a reference to the I3C target controller based on the device name of
+   the controller.
+
+* i3c_target_ctrl_put()
+
+   Release the reference to the I3C target controller obtained using
+   i3c_target_ctrl_get()
+
+* i3c_target_ctrl_add_func()
+
+   Add a I3C target function to a I3C target controller.
+
+* i3c_target_ctrl_remove_func()
+
+   Remove the I3C target function from I3C target controller.
+
+I3C Target Function Library
+----------------------------------
+
+The I3C Target Function library provides APIs to be used by the function driver
+and the Controller library to provide target mode functionality.
+
+I3C Target Function APIs for the I3C Target Function Driver
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This section lists the APIs that the I3C Target core provides to be used
+by the I3C target function driver.
+
+* i3c_target_func_register_driver()
+
+   The I3C Target Function driver should implement the following ops:
+	 * bind: ops to perform when a Controller device has been bound to
+	   Function device
+	 * unbind: ops to perform when a binding has been lost between a
+	   Controller device and Function device
+
+  The I3C Function driver can then register the I3C Function driver by using
+  i3c_target_func_register_driver().
+
+* i3c_target_func_unregister_driver()
+
+  The I3C Function driver can unregister the I3C Function driver by using
+  i3c_epf_unregister_driver().
+
+APIs for the I3C Target Controller Library
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This section lists the APIs that the I3C Target core provides to be used by the
+I3C target controller library.
+
+Other I3C Target APIs
+~~~~~~~~~~~~~~~~~~~~
+
+There are other APIs provided by the Function library. These are used to notify
+the function driver when the Function device is bound to the EPC device.
+i3c-cfs.c can be used as reference for using these APIs.
+
+* i3c_target_func_create()
+
+   Create a new I3C Function device by passing the name of the I3C EPF device.
+   This name will be used to bind the Function device to a Function driver.
+
+* i3c_target_func_destroy()
+
+   Destroy the created I3C Function device.
+
+* i3c_target_func_bind()
+
+   i3c_target_func_bind() should be invoked when the EPF device has been bound
+   to a Controller device.
+
+* i3c_target_func_unbind()
+
+   i3c_target_func_unbind() should be invoked when the binding between EPC
+   device and function device is lost.
diff --git a/Documentation/driver-api/i3c/target/i3c-tty-howto.rst b/Documentation/driver-api/i3c/target/i3c-tty-howto.rst
new file mode 100644
index 0000000000000..43a129b18e938
--- /dev/null
+++ b/Documentation/driver-api/i3c/target/i3c-tty-howto.rst
@@ -0,0 +1,109 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+===================
+I3C TTY User Guide
+===================
+
+:Author: Frank Li <Frank.Li@nxp.com>
+
+This document is a guide to help users use i3c-target-tty function driver and
+i3ctty master driver for testing I3C. The list of steps to be followed in the
+master side and target side is given below.
+
+Endpoint Device
+===============
+
+Endpoint Controller Devices
+---------------------------
+
+To find the list of target controller devices in the system::
+
+	# ls  /sys/class/i3c_target/
+	  44330000.i3c-target
+
+If CONFIG_I3C_SLAVE_CONFIGFS is enabled::
+
+	# ls /sys/kernel/config/i3c_target/controllers/
+	  44330000.i3c-target
+
+
+Endpoint Function Drivers
+-------------------------
+
+To find the list of target function drivers in the system::
+
+	# ls /sys/bus/i3c_target_func/drivers
+	  tty
+
+If CONFIG_I3C_SLAVE_CONFIGFS is enabled::
+
+	# ls /sys/kernel/config/i3c_target/functions
+	  tty
+
+
+Creating i3c-target-tty Device
+----------------------------
+
+I3C target function device can be created using the configfs. To create
+i3c-target-tty device, the following commands can be used::
+
+	# mount -t configfs none /sys/kernel/config
+	# cd /sys/kernel/config/i3c_target/
+	# mkdir functions/tty/func1
+
+The "mkdir func1" above creates the i3c-target-tty function device that will
+be probed by i3c tty driver.
+
+The I3C target framework populates the directory with the following
+configurable fields::
+
+	# ls functions/tty/func1
+	bcr  dcr  ext_id  instance_id  max_read_len  max_write_len
+	part_id  vendor_id  vendor_info
+
+The I3C target function driver populates these entries with default values when
+the device is bound to the driver. The i3c-target-tty driver populates vendorid
+with 0xffff and interrupt_pin with 0x0001::
+
+	# cat functions/tty/func1/vendor_id
+	  0x0
+
+Configuring i3c-target-tty Device
+-------------------------------
+
+The user can configure the i3c-target-tty device using configfs entry. In order
+to change the vendorid, the following commands can be used::
+
+	# echo 0x011b > functions/tty/func1/vendor_id
+	# echo 0x1000 > functions/tty/func1/part_id
+	# echo 0x6 > functions/tty/t/bcr
+
+Binding i3c-target-tty Device to target Controller
+------------------------------------------------
+
+In order for the target function device to be useful, it has to be bound to a
+I3C target controller driver. Use the configfs to bind the function device to
+one of the controller driver present in the system::
+
+	# ln -s functions/tty/func1 controllers/44330000.i3c-target/
+
+I3C Master Device
+================
+
+Check I3C tty device is probed
+
+	# ls /sys/bus/i3c/devices/0-23610000000
+	0-23610000000:0  bcr  dcr  driver  dynamic_address  hdrcap
+	modalias  pid  power  subsystem  tty  uevent
+
+Using Target TTY function Device
+-----------------------------------
+
+Host side:
+	cat /dev/ttyI3C0
+Target side
+	echo abc >/dev/ttyI3C0
+
+You will see "abc" show at console.
+
+You can use other tty tool to test I3C target tty device.
diff --git a/Documentation/driver-api/i3c/target/index.rst b/Documentation/driver-api/i3c/target/index.rst
new file mode 100644
index 0000000000000..56eabfae83aa4
--- /dev/null
+++ b/Documentation/driver-api/i3c/target/index.rst
@@ -0,0 +1,13 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+======================
+I3C Target Framework
+======================
+
+.. toctree::
+   :maxdepth: 2
+
+   i3c-target
+   i3c-target-cfs
+   i3c-tty-howto
+