docs: i2c: summary: document use of inclusive language

We now have the updated I2C specs and our own Code of Conduct, so we
have all we need to switch over to the inclusive terminology. Define
them here.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Easwar Hariharan <eahariha@linux.microsoft.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Author: Wolfram Sang

Documentation/i2c/i2c_bus.svg

@@ -31,15 +31,16 @@ implement all the common SMBus protocol semantics or messages.
 Terminology
 ===========
 
-Using the terminology from the official documentation, the I2C bus connects
-one or more *master* chips and one or more *slave* chips.
+The I2C bus connects one or more *controller* chips and one or more *target*
+chips.
+
 
 .. kernel-figure::  i2c_bus.svg
-   :alt:    Simple I2C bus with one master and 3 slaves
+   :alt:    Simple I2C bus with one controller and 3 targets
 
    Simple I2C bus
 
-A **master** chip is a node that starts communications with slaves. In the
+A **controller** chip is a node that starts communications with targets. In the
 Linux kernel implementation it is called an **adapter** or bus. Adapter
 drivers are in the ``drivers/i2c/busses/`` subdirectory.
 
@@ -48,12 +49,22 @@ whole class of I2C adapters. Each specific adapter driver either depends on
 an algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes
 its own implementation.
 
-A **slave** chip is a node that responds to communications when addressed
-by the master. In Linux it is called a **client**. Client drivers are kept
+A **target** chip is a node that responds to communications when addressed
+by the controller. In Linux it is called a **client**. Client drivers are kept
 in a directory specific to the feature they provide, for example
 ``drivers/media/gpio/`` for GPIO expanders and ``drivers/media/i2c/`` for
 video-related chips.
 
 For the example configuration in figure, you will need a driver for your
 I2C adapter, and drivers for your I2C devices (usually one driver for each
 device).
+
+Outdated terminology
+--------------------
+
+In earlier I2C specifications, controller was named "master" and target was
+named "slave". These terms have been obsoleted with v7 of the specification and
+their use is also discouraged by the Linux Kernel Code of Conduct. You may
+still find them in references to documentation which has not been updated. The
+general attitude, however, is to use the inclusive terms: controller and
+target. Work to replace the old terminology in the Linux Kernel is on-going.