Device connections

Introduction

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

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

void * device_connection_find_match(struct device * dev, const char * con_id, void * data, void *(*match) (struct device_connection *con, int ep, void *data)

Find physical connection to a device

Parameters

struct device * dev
Device with the connection
const char * con_id
Identifier for the connection
void * data
Data for the match function
void *(*)(struct device_connection *con, int ep, void *data) match
Function to check and convert the connection description

Description

Find a connection with unique identifier con_id between dev and another device. match will be used to convert the connection description to data the caller is expecting to be returned.

struct device * device_connection_find(struct device * dev, const char * con_id)

Find two devices connected together

Parameters

struct device * dev
Device with the connection
const char * con_id
Identifier for the connection

Description

Find a connection with unique identifier con_id between dev and another device. On success returns handle to the device that is connected to dev, with the reference count for the found device incremented. Returns NULL if no matching connection was found, or ERR_PTR(-EPROBE_DEFER) when a connection was found but the other device has not been enumerated yet.

void device_connection_add(struct device_connection * con)

Register a connection description

Parameters

struct device_connection * con
The connection description to be registered
void device_connection_remove(struct device_connection * con)

Unregister connection description

Parameters

struct device_connection * con
The connection description to be unregistered