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  1                             PHY SUBSYSTEM
  2                   Kishon Vijay Abraham I <>
  4 This document explains the Generic PHY Framework along with the APIs provided,
  5 and how-to-use.
  7 1. Introduction
  9 *PHY* is the abbreviation for physical layer. It is used to connect a device
 10 to the physical medium e.g., the USB controller has a PHY to provide functions
 11 such as serialization, de-serialization, encoding, decoding and is responsible
 12 for obtaining the required data transmission rate. Note that some USB
 13 controllers have PHY functionality embedded into it and others use an external
 14 PHY. Other peripherals that use PHY include Wireless LAN, Ethernet,
 15 SATA etc.
 17 The intention of creating this framework is to bring the PHY drivers spread
 18 all over the Linux kernel to drivers/phy to increase code re-use and for
 19 better code maintainability.
 21 This framework will be of use only to devices that use external PHY (PHY
 22 functionality is not embedded within the controller).
 24 2. Registering/Unregistering the PHY provider
 26 PHY provider refers to an entity that implements one or more PHY instances.
 27 For the simple case where the PHY provider implements only a single instance of
 28 the PHY, the framework provides its own implementation of of_xlate in
 29 of_phy_simple_xlate. If the PHY provider implements multiple instances, it
 30 should provide its own implementation of of_xlate. of_xlate is used only for
 31 dt boot case.
 33 #define of_phy_provider_register(dev, xlate)    \
 34         __of_phy_provider_register((dev), NULL, THIS_MODULE, (xlate))
 36 #define devm_of_phy_provider_register(dev, xlate)       \
 37         __devm_of_phy_provider_register((dev), NULL, THIS_MODULE, (xlate))
 39 of_phy_provider_register and devm_of_phy_provider_register macros can be used to
 40 register the phy_provider and it takes device and of_xlate as
 41 arguments. For the dt boot case, all PHY providers should use one of the above
 42 2 macros to register the PHY provider.
 44 Often the device tree nodes associated with a PHY provider will contain a set
 45 of children that each represent a single PHY. Some bindings may nest the child
 46 nodes within extra levels for context and extensibility, in which case the low
 47 level of_phy_provider_register_full() and devm_of_phy_provider_register_full()
 48 macros can be used to override the node containing the children.
 50 #define of_phy_provider_register_full(dev, children, xlate) \
 51         __of_phy_provider_register(dev, children, THIS_MODULE, xlate)
 53 #define devm_of_phy_provider_register_full(dev, children, xlate) \
 54         __devm_of_phy_provider_register_full(dev, children, THIS_MODULE, xlate)
 56 void devm_of_phy_provider_unregister(struct device *dev,
 57         struct phy_provider *phy_provider);
 58 void of_phy_provider_unregister(struct phy_provider *phy_provider);
 60 devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to
 61 unregister the PHY.
 63 3. Creating the PHY
 65 The PHY driver should create the PHY in order for other peripheral controllers
 66 to make use of it. The PHY framework provides 2 APIs to create the PHY.
 68 struct phy *phy_create(struct device *dev, struct device_node *node,
 69                        const struct phy_ops *ops);
 70 struct phy *devm_phy_create(struct device *dev, struct device_node *node,
 71                             const struct phy_ops *ops);
 73 The PHY drivers can use one of the above 2 APIs to create the PHY by passing
 74 the device pointer and phy ops.
 75 phy_ops is a set of function pointers for performing PHY operations such as
 76 init, exit, power_on and power_off.
 78 Inorder to dereference the private data (in phy_ops), the phy provider driver
 79 can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
 80 phy_ops to get back the private data.
 82 4. Getting a reference to the PHY
 84 Before the controller can make use of the PHY, it has to get a reference to
 85 it. This framework provides the following APIs to get a reference to the PHY.
 87 struct phy *phy_get(struct device *dev, const char *string);
 88 struct phy *phy_optional_get(struct device *dev, const char *string);
 89 struct phy *devm_phy_get(struct device *dev, const char *string);
 90 struct phy *devm_phy_optional_get(struct device *dev, const char *string);
 91 struct phy *devm_of_phy_get_by_index(struct device *dev, struct device_node *np,
 92                                      int index);
 94 phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can
 95 be used to get the PHY. In the case of dt boot, the string arguments
 96 should contain the phy name as given in the dt data and in the case of
 97 non-dt boot, it should contain the label of the PHY.  The two
 98 devm_phy_get associates the device with the PHY using devres on
 99 successful PHY get. On driver detach, release function is invoked on
100 the the devres data and devres data is freed. phy_optional_get and
101 devm_phy_optional_get should be used when the phy is optional. These
102 two functions will never return -ENODEV, but instead returns NULL when
103 the phy cannot be found.Some generic drivers, such as ehci, may use multiple
104 phys and for such drivers referencing phy(s) by name(s) does not make sense. In
105 this case, devm_of_phy_get_by_index can be used to get a phy reference based on
106 the index.
108 It should be noted that NULL is a valid phy reference. All phy
109 consumer calls on the NULL phy become NOPs. That is the release calls,
110 the phy_init() and phy_exit() calls, and phy_power_on() and
111 phy_power_off() calls are all NOP when applied to a NULL phy. The NULL
112 phy is useful in devices for handling optional phy devices.
114 5. Releasing a reference to the PHY
116 When the controller no longer needs the PHY, it has to release the reference
117 to the PHY it has obtained using the APIs mentioned in the above section. The
118 PHY framework provides 2 APIs to release a reference to the PHY.
120 void phy_put(struct phy *phy);
121 void devm_phy_put(struct device *dev, struct phy *phy);
123 Both these APIs are used to release a reference to the PHY and devm_phy_put
124 destroys the devres associated with this PHY.
126 6. Destroying the PHY
128 When the driver that created the PHY is unloaded, it should destroy the PHY it
129 created using one of the following 2 APIs.
131 void phy_destroy(struct phy *phy);
132 void devm_phy_destroy(struct device *dev, struct phy *phy);
134 Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
135 associated with this PHY.
137 7. PM Runtime
139 This subsystem is pm runtime enabled. So while creating the PHY,
140 pm_runtime_enable of the phy device created by this subsystem is called and
141 while destroying the PHY, pm_runtime_disable is called. Note that the phy
142 device created by this subsystem will be a child of the device that calls
143 phy_create (PHY provider device).
145 So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
146 pm_runtime_get_sync of PHY provider device because of parent-child relationship.
147 It should also be noted that phy_power_on and phy_power_off performs
148 phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
149 There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
150 phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
151 phy_pm_runtime_forbid for performing PM operations.
153 8. PHY Mappings
155 In order to get reference to a PHY without help from DeviceTree, the framework
156 offers lookups which can be compared to clkdev that allow clk structures to be
157 bound to devices. A lookup can be made be made during runtime when a handle to
158 the struct phy already exists.
160 The framework offers the following API for registering and unregistering the
161 lookups.
163 int phy_create_lookup(struct phy *phy, const char *con_id, const char *dev_id);
164 void phy_remove_lookup(struct phy *phy, const char *con_id, const char *dev_id);
166 9. DeviceTree Binding
168 The documentation for PHY dt binding can be found @
169 Documentation/devicetree/bindings/phy/phy-bindings.txt

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