Documentation/phy.txt

   1                             PHY SUBSYSTEM
   2                   Kishon Vijay Abraham I <kishon@ti.com>
   3
   4 This document explains the Generic PHY Framework along with the APIs provided,
   5 and how-to-use.
   6
   7 1. Introduction
   8
   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.
  16
  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.
  20
  21 This framework will be of use only to devices that use external PHY (PHY
  22 functionality is not embedded within the controller).
  23
  24 2. Registering/Unregistering the PHY provider
  25
  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.
  32
  33 #define of_phy_provider_register(dev, xlate)    \
  34         __of_phy_provider_register((dev), THIS_MODULE, (xlate))
  35
  36 #define devm_of_phy_provider_register(dev, xlate)       \
  37         __devm_of_phy_provider_register((dev), THIS_MODULE, (xlate))
  38
  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.
  43
  44 void devm_of_phy_provider_unregister(struct device *dev,
  45         struct phy_provider *phy_provider);
  46 void of_phy_provider_unregister(struct phy_provider *phy_provider);
  47
  48 devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to
  49 unregister the PHY.
  50
  51 3. Creating the PHY
  52
  53 The PHY driver should create the PHY in order for other peripheral controllers
  54 to make use of it. The PHY framework provides 2 APIs to create the PHY.
  55
  56 struct phy *phy_create(struct device *dev, struct device_node *node,
  57                        const struct phy_ops *ops);
  58 struct phy *devm_phy_create(struct device *dev, struct device_node *node,
  59                             const struct phy_ops *ops);
  60
  61 The PHY drivers can use one of the above 2 APIs to create the PHY by passing
  62 the device pointer and phy ops.
  63 phy_ops is a set of function pointers for performing PHY operations such as
  64 init, exit, power_on and power_off.
  65
  66 Inorder to dereference the private data (in phy_ops), the phy provider driver
  67 can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
  68 phy_ops to get back the private data.
  69
  70 4. Getting a reference to the PHY
  71
  72 Before the controller can make use of the PHY, it has to get a reference to
  73 it. This framework provides the following APIs to get a reference to the PHY.
  74
  75 struct phy *phy_get(struct device *dev, const char *string);
  76 struct phy *phy_optional_get(struct device *dev, const char *string);
  77 struct phy *devm_phy_get(struct device *dev, const char *string);
  78 struct phy *devm_phy_optional_get(struct device *dev, const char *string);
  79 struct phy *devm_of_phy_get_by_index(struct device *dev, struct device_node *np,
  80                                      int index);
  81
  82 phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can
  83 be used to get the PHY. In the case of dt boot, the string arguments
  84 should contain the phy name as given in the dt data and in the case of
  85 non-dt boot, it should contain the label of the PHY.  The two
  86 devm_phy_get associates the device with the PHY using devres on
  87 successful PHY get. On driver detach, release function is invoked on
  88 the the devres data and devres data is freed. phy_optional_get and
  89 devm_phy_optional_get should be used when the phy is optional. These
  90 two functions will never return -ENODEV, but instead returns NULL when
  91 the phy cannot be found.Some generic drivers, such as ehci, may use multiple
  92 phys and for such drivers referencing phy(s) by name(s) does not make sense. In
  93 this case, devm_of_phy_get_by_index can be used to get a phy reference based on
  94 the index.
  95
  96 It should be noted that NULL is a valid phy reference. All phy
  97 consumer calls on the NULL phy become NOPs. That is the release calls,
  98 the phy_init() and phy_exit() calls, and phy_power_on() and
  99 phy_power_off() calls are all NOP when applied to a NULL phy. The NULL
 100 phy is useful in devices for handling optional phy devices.
 101
 102 5. Releasing a reference to the PHY
 103
 104 When the controller no longer needs the PHY, it has to release the reference
 105 to the PHY it has obtained using the APIs mentioned in the above section. The
 106 PHY framework provides 2 APIs to release a reference to the PHY.
 107
 108 void phy_put(struct phy *phy);
 109 void devm_phy_put(struct device *dev, struct phy *phy);
 110
 111 Both these APIs are used to release a reference to the PHY and devm_phy_put
 112 destroys the devres associated with this PHY.
 113
 114 6. Destroying the PHY
 115
 116 When the driver that created the PHY is unloaded, it should destroy the PHY it
 117 created using one of the following 2 APIs.
 118
 119 void phy_destroy(struct phy *phy);
 120 void devm_phy_destroy(struct device *dev, struct phy *phy);
 121
 122 Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
 123 associated with this PHY.
 124
 125 7. PM Runtime
 126
 127 This subsystem is pm runtime enabled. So while creating the PHY,
 128 pm_runtime_enable of the phy device created by this subsystem is called and
 129 while destroying the PHY, pm_runtime_disable is called. Note that the phy
 130 device created by this subsystem will be a child of the device that calls
 131 phy_create (PHY provider device).
 132
 133 So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
 134 pm_runtime_get_sync of PHY provider device because of parent-child relationship.
 135 It should also be noted that phy_power_on and phy_power_off performs
 136 phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
 137 There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
 138 phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
 139 phy_pm_runtime_forbid for performing PM operations.
 140
 141 8. PHY Mappings
 142
 143 In order to get reference to a PHY without help from DeviceTree, the framework
 144 offers lookups which can be compared to clkdev that allow clk structures to be
 145 bound to devices. A lookup can be made be made during runtime when a handle to
 146 the struct phy already exists.
 147
 148 The framework offers the following API for registering and unregistering the
 149 lookups.
 150
 151 int phy_create_lookup(struct phy *phy, const char *con_id, const char *dev_id);
 152 void phy_remove_lookup(struct phy *phy, const char *con_id, const char *dev_id);
 153
 154 9. DeviceTree Binding
 155
 156 The documentation for PHY dt binding can be found @
 157 Documentation/devicetree/bindings/phy/phy-bindings.txt