linux/Documentation/phy.txt
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   1                            PHY SUBSYSTEM
   2                  Kishon Vijay Abraham I <kishon@ti.com>
   3
   4This document explains the Generic PHY Framework along with the APIs provided,
   5and how-to-use.
   6
   71. Introduction
   8
   9*PHY* is the abbreviation for physical layer. It is used to connect a device
  10to the physical medium e.g., the USB controller has a PHY to provide functions
  11such as serialization, de-serialization, encoding, decoding and is responsible
  12for obtaining the required data transmission rate. Note that some USB
  13controllers have PHY functionality embedded into it and others use an external
  14PHY. Other peripherals that use PHY include Wireless LAN, Ethernet,
  15SATA etc.
  16
  17The intention of creating this framework is to bring the PHY drivers spread
  18all over the Linux kernel to drivers/phy to increase code re-use and for
  19better code maintainability.
  20
  21This framework will be of use only to devices that use external PHY (PHY
  22functionality is not embedded within the controller).
  23
  242. Registering/Unregistering the PHY provider
  25
  26PHY provider refers to an entity that implements one or more PHY instances.
  27For the simple case where the PHY provider implements only a single instance of
  28the PHY, the framework provides its own implementation of of_xlate in
  29of_phy_simple_xlate. If the PHY provider implements multiple instances, it
  30should provide its own implementation of of_xlate. of_xlate is used only for
  31dt boot case.
  32
  33#define of_phy_provider_register(dev, xlate)    \
  34        __of_phy_provider_register((dev), NULL, THIS_MODULE, (xlate))
  35
  36#define devm_of_phy_provider_register(dev, xlate)       \
  37        __devm_of_phy_provider_register((dev), NULL, THIS_MODULE, (xlate))
  38
  39of_phy_provider_register and devm_of_phy_provider_register macros can be used to
  40register the phy_provider and it takes device and of_xlate as
  41arguments. For the dt boot case, all PHY providers should use one of the above
  422 macros to register the PHY provider.
  43
  44Often the device tree nodes associated with a PHY provider will contain a set
  45of children that each represent a single PHY. Some bindings may nest the child
  46nodes within extra levels for context and extensibility, in which case the low
  47level of_phy_provider_register_full() and devm_of_phy_provider_register_full()
  48macros can be used to override the node containing the children.
  49
  50#define of_phy_provider_register_full(dev, children, xlate) \
  51        __of_phy_provider_register(dev, children, THIS_MODULE, xlate)
  52
  53#define devm_of_phy_provider_register_full(dev, children, xlate) \
  54        __devm_of_phy_provider_register_full(dev, children, THIS_MODULE, xlate)
  55
  56void devm_of_phy_provider_unregister(struct device *dev,
  57        struct phy_provider *phy_provider);
  58void of_phy_provider_unregister(struct phy_provider *phy_provider);
  59
  60devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to
  61unregister the PHY.
  62
  633. Creating the PHY
  64
  65The PHY driver should create the PHY in order for other peripheral controllers
  66to make use of it. The PHY framework provides 2 APIs to create the PHY.
  67
  68struct phy *phy_create(struct device *dev, struct device_node *node,
  69                       const struct phy_ops *ops);
  70struct phy *devm_phy_create(struct device *dev, struct device_node *node,
  71                            const struct phy_ops *ops);
  72
  73The PHY drivers can use one of the above 2 APIs to create the PHY by passing
  74the device pointer and phy ops.
  75phy_ops is a set of function pointers for performing PHY operations such as
  76init, exit, power_on and power_off.
  77
  78Inorder to dereference the private data (in phy_ops), the phy provider driver
  79can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
  80phy_ops to get back the private data.
  81
  824. Getting a reference to the PHY
  83
  84Before the controller can make use of the PHY, it has to get a reference to
  85it. This framework provides the following APIs to get a reference to the PHY.
  86
  87struct phy *phy_get(struct device *dev, const char *string);
  88struct phy *phy_optional_get(struct device *dev, const char *string);
  89struct phy *devm_phy_get(struct device *dev, const char *string);
  90struct phy *devm_phy_optional_get(struct device *dev, const char *string);
  91struct phy *devm_of_phy_get_by_index(struct device *dev, struct device_node *np,
  92                                     int index);
  93
  94phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can
  95be used to get the PHY. In the case of dt boot, the string arguments
  96should contain the phy name as given in the dt data and in the case of
  97non-dt boot, it should contain the label of the PHY.  The two
  98devm_phy_get associates the device with the PHY using devres on
  99successful PHY get. On driver detach, release function is invoked on
 100the the devres data and devres data is freed. phy_optional_get and
 101devm_phy_optional_get should be used when the phy is optional. These
 102two functions will never return -ENODEV, but instead returns NULL when
 103the phy cannot be found.Some generic drivers, such as ehci, may use multiple
 104phys and for such drivers referencing phy(s) by name(s) does not make sense. In
 105this case, devm_of_phy_get_by_index can be used to get a phy reference based on
 106the index.
 107
 108It should be noted that NULL is a valid phy reference. All phy
 109consumer calls on the NULL phy become NOPs. That is the release calls,
 110the phy_init() and phy_exit() calls, and phy_power_on() and
 111phy_power_off() calls are all NOP when applied to a NULL phy. The NULL
 112phy is useful in devices for handling optional phy devices.
 113
 1145. Releasing a reference to the PHY
 115
 116When the controller no longer needs the PHY, it has to release the reference
 117to the PHY it has obtained using the APIs mentioned in the above section. The
 118PHY framework provides 2 APIs to release a reference to the PHY.
 119
 120void phy_put(struct phy *phy);
 121void devm_phy_put(struct device *dev, struct phy *phy);
 122
 123Both these APIs are used to release a reference to the PHY and devm_phy_put
 124destroys the devres associated with this PHY.
 125
 1266. Destroying the PHY
 127
 128When the driver that created the PHY is unloaded, it should destroy the PHY it
 129created using one of the following 2 APIs.
 130
 131void phy_destroy(struct phy *phy);
 132void devm_phy_destroy(struct device *dev, struct phy *phy);
 133
 134Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
 135associated with this PHY.
 136
 1377. PM Runtime
 138
 139This subsystem is pm runtime enabled. So while creating the PHY,
 140pm_runtime_enable of the phy device created by this subsystem is called and
 141while destroying the PHY, pm_runtime_disable is called. Note that the phy
 142device created by this subsystem will be a child of the device that calls
 143phy_create (PHY provider device).
 144
 145So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
 146pm_runtime_get_sync of PHY provider device because of parent-child relationship.
 147It should also be noted that phy_power_on and phy_power_off performs
 148phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
 149There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
 150phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
 151phy_pm_runtime_forbid for performing PM operations.
 152
 1538. PHY Mappings
 154
 155In order to get reference to a PHY without help from DeviceTree, the framework
 156offers lookups which can be compared to clkdev that allow clk structures to be
 157bound to devices. A lookup can be made be made during runtime when a handle to
 158the struct phy already exists.
 159
 160The framework offers the following API for registering and unregistering the
 161lookups.
 162
 163int phy_create_lookup(struct phy *phy, const char *con_id, const char *dev_id);
 164void phy_remove_lookup(struct phy *phy, const char *con_id, const char *dev_id);
 165
 1669. DeviceTree Binding
 167
 168The documentation for PHY dt binding can be found @
 169Documentation/devicetree/bindings/phy/phy-bindings.txt
 170