Documentation: Remove device connection documentation

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Device connections

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Introduction

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Devices often have connections to other devices that are outside of the direct

child/parent relationship. A serial or network communication controller, which

could be a PCI device, may need to be able to get a reference to its PHY

component, which could be attached for example to the I2C bus. Some device

drivers need to be able to control the clocks or the GPIOs for their devices,

and so on.

Device connections are generic descriptions of any type of connection between

two separate devices.

Device connections alone do not create a dependency between the two devices.

They are only descriptions which are not tied to either of the devices directly.

A dependency between the two devices exists only if one of the two endpoint

devices requests a reference to the other. The descriptions themselves can be

defined in firmware (not yet supported) or they can be built-in.

Usage

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Device connections should exist before device ``->probe`` callback is called for

either endpoint device in the description. If the connections are defined in

firmware, this is not a problem. It should be considered if the connection

descriptions are "built-in", and need to be added separately.

The connection description consists of the names of the two devices with the

connection, i.e. the endpoints, and unique identifier for the connection which

is needed if there are multiple connections between the two devices.

After a description exists, the devices in it can request reference to the other

endpoint device, or they can request the description itself.

API

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.. kernel-doc:: drivers/base/devcon.c

   :functions: device_connection_find_match device_connection_find device_connection_add device_connection_remove

   pm/index

   clk

   device-io

   device_connection

   dma-buf

   device_link

   component