linux-imx

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PHY subsystem

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:Author: Kishon Vijay Abraham I <kishon@ti.com>

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This document explains the Generic PHY Framework along with the APIs provided,

and how-to-use.

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Introduction

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*PHY* is the abbreviation for physical layer. It is used to connect a device

to the physical medium e.g., the USB controller has a PHY to provide functions

such as serialization, de-serialization, encoding, decoding and is responsible

for obtaining the required data transmission rate. Note that some USB

controllers have PHY functionality embedded into it and others use an external

PHY. Other peripherals that use PHY include Wireless LAN, Ethernet,

SATA etc.

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The intention of creating this framework is to bring the PHY drivers spread

all over the Linux kernel to drivers/phy to increase code re-use and for

better code maintainability.

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This framework will be of use only to devices that use external PHY (PHY

functionality is not embedded within the controller).

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Registering/Unregistering the PHY provider

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PHY provider refers to an entity that implements one or more PHY instances.

For the simple case where the PHY provider implements only a single instance of

the PHY, the framework provides its own implementation of of_xlate in

of_phy_simple_xlate. If the PHY provider implements multiple instances, it

should provide its own implementation of of_xlate. of_xlate is used only for

dt boot case.

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::

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    #define of_phy_provider_register(dev, xlate)    \

        __of_phy_provider_register((dev), NULL, THIS_MODULE, (xlate))

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    #define devm_of_phy_provider_register(dev, xlate)       \

        __devm_of_phy_provider_register((dev), NULL, THIS_MODULE,

                        (xlate))

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of_phy_provider_register and devm_of_phy_provider_register macros can be used to

register the phy_provider and it takes device and of_xlate as

arguments. For the dt boot case, all PHY providers should use one of the above

2 macros to register the PHY provider.

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Often the device tree nodes associated with a PHY provider will contain a set

of children that each represent a single PHY. Some bindings may nest the child

nodes within extra levels for context and extensibility, in which case the low

level of_phy_provider_register_full() and devm_of_phy_provider_register_full()

macros can be used to override the node containing the children.

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::

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    #define of_phy_provider_register_full(dev, children, xlate) \

        __of_phy_provider_register(dev, children, THIS_MODULE, xlate)

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    #define devm_of_phy_provider_register_full(dev, children, xlate) \

        __devm_of_phy_provider_register_full(dev, children,

                             THIS_MODULE, xlate)

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    void devm_of_phy_provider_unregister(struct device *dev,

        struct phy_provider *phy_provider);

    void of_phy_provider_unregister(struct phy_provider *phy_provider);

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devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to

unregister the PHY.

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Creating the PHY

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The PHY driver should create the PHY in order for other peripheral controllers

to make use of it. The PHY framework provides 2 APIs to create the PHY.

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::

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    struct phy *phy_create(struct device *dev, struct device_node *node,

                   const struct phy_ops *ops);

    struct phy *devm_phy_create(struct device *dev,

                    struct device_node *node,

                    const struct phy_ops *ops);

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The PHY drivers can use one of the above 2 APIs to create the PHY by passing

the device pointer and phy ops.

phy_ops is a set of function pointers for performing PHY operations such as

init, exit, power_on and power_off.

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