44 lines
1.8 KiB
ReStructuredText
44 lines
1.8 KiB
ReStructuredText
==================
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Device connections
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==================
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Introduction
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------------
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Devices often have connections to other devices that are outside of the direct
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child/parent relationship. A serial or network communication controller, which
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could be a PCI device, may need to be able to get a reference to its PHY
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component, which could be attached for example to the I2C bus. Some device
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drivers need to be able to control the clocks or the GPIOs for their devices,
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and so on.
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Device connections are generic descriptions of any type of connection between
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two separate devices.
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Device connections alone do not create a dependency between the two devices.
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They are only descriptions which are not tied to either of the devices directly.
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A dependency between the two devices exists only if one of the two endpoint
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devices requests a reference to the other. The descriptions themselves can be
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defined in firmware (not yet supported) or they can be built-in.
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Usage
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-----
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Device connections should exist before device ``->probe`` callback is called for
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either endpoint device in the description. If the connections are defined in
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firmware, this is not a problem. It should be considered if the connection
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descriptions are "built-in", and need to be added separately.
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The connection description consists of the names of the two devices with the
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connection, i.e. the endpoints, and unique identifier for the connection which
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is needed if there are multiple connections between the two devices.
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After a description exists, the devices in it can request reference to the other
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endpoint device, or they can request the description itself.
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API
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---
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.. kernel-doc:: drivers/base/devcon.c
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:functions: device_connection_find_match device_connection_find device_connection_add device_connection_remove
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