docs: i2c: summary: be clearer with 'controller/target' and 'adapter/client' pairs

This not only includes rewording, but also where to put which emphasis
on terms in this document.

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/summary.rst

@@ -31,38 +31,45 @@ implement all the common SMBus protocol semantics or messages.
 Terminology
 ===========
 
-The I2C bus connects one or more *controller* chips and one or more *target*
-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 controller and 3 targets
 
    Simple I2C bus
 
 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.
+Linux kernel implementation it is also called an "adapter" or "bus". Controller
+drivers are usually in the ``drivers/i2c/busses/`` subdirectory.
 
-An **algorithm** contains general code that can be used to implement a
-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.
+An **algorithm** contains general code that can be used to implement a whole
+class of I2C controllers. Each specific controller driver either depends on an
+algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes its
+own implementation.
 
 A **target** chip is a node that responds to communications when addressed by a
-controller. In the Linux kernel implementation it is called a **client**. While
-targets are usually separate external chips, Linux can also act as a target
-(needs hardware support) and respond to another controller on the bus. This is
-then called a **local target**. In contrast, an external chip is called a
-**remote target**.
+controller. In the Linux kernel implementation it is also called a "client".
+While targets are usually separate external chips, Linux can also act as a
+target (needs hardware support) and respond to another controller on the bus.
+This is then called a **local target**. In contrast, an external chip is called
+a **remote target**.
 
 Target drivers are kept in a directory specific to the feature they provide,
 for example ``drivers/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).
+For the example configuration in the figure above, you will need one driver for
+the I2C controller, and drivers for your I2C targets. Usually one driver for
+each target.
+
+Synonyms
+--------
+
+As mentioned above, the Linux I2C implementation historically uses the terms
+"adapter" for controller and "client" for target. A number of data structures
+have these synonyms in their name. So, when discussing implementation details,
+you should be aware of these terms as well. The official wording is preferred,
+though.
 
 Outdated terminology
 --------------------