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_init_data *init_data);
  59 struct phy *devm_phy_create(struct device *dev, struct device_node *node,
  60                             const struct phy_ops *ops,
  61                             struct phy_init_data *init_data);
  62
  63 The PHY drivers can use one of the above 2 APIs to create the PHY by passing
  64 the device pointer, phy ops and init_data.
  65 phy_ops is a set of function pointers for performing PHY operations such as
  66 init, exit, power_on and power_off. *init_data* is mandatory to get a reference
  67 to the PHY in the case of non-dt boot. See section *Board File Initialization*
  68 on how init_data should be used.
  69
  70 Inorder to dereference the private data (in phy_ops), the phy provider driver
  71 can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
  72 phy_ops to get back the private data.
  73
  74 4. Getting a reference to the PHY
  75
  76 Before the controller can make use of the PHY, it has to get a reference to
  77 it. This framework provides the following APIs to get a reference to the PHY.
  78
  79 struct phy *phy_get(struct device *dev, const char *string);
  80 struct phy *phy_optional_get(struct device *dev, const char *string);
  81 struct phy *devm_phy_get(struct device *dev, const char *string);
  82 struct phy *devm_phy_optional_get(struct device *dev, const char *string);
  83
  84 phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can
  85 be used to get the PHY. In the case of dt boot, the string arguments
  86 should contain the phy name as given in the dt data and in the case of
  87 non-dt boot, it should contain the label of the PHY.  The two
  88 devm_phy_get associates the device with the PHY using devres on
  89 successful PHY get. On driver detach, release function is invoked on
  90 the the devres data and devres data is freed. phy_optional_get and
  91 devm_phy_optional_get should be used when the phy is optional. These
  92 two functions will never return -ENODEV, but instead returns NULL when
  93 the phy cannot be found.
  94
  95 It should be noted that NULL is a valid phy reference. All phy
  96 consumer calls on the NULL phy become NOPs. That is the release calls,
  97 the phy_init() and phy_exit() calls, and phy_power_on() and
  98 phy_power_off() calls are all NOP when applied to a NULL phy. The NULL
  99 phy is useful in devices for handling optional phy devices.
 100
 101 5. Releasing a reference to the PHY
 102
 103 When the controller no longer needs the PHY, it has to release the reference
 104 to the PHY it has obtained using the APIs mentioned in the above section. The
 105 PHY framework provides 2 APIs to release a reference to the PHY.
 106
 107 void phy_put(struct phy *phy);
 108 void devm_phy_put(struct device *dev, struct phy *phy);
 109
 110 Both these APIs are used to release a reference to the PHY and devm_phy_put
 111 destroys the devres associated with this PHY.
 112
 113 6. Destroying the PHY
 114
 115 When the driver that created the PHY is unloaded, it should destroy the PHY it
 116 created using one of the following 2 APIs.
 117
 118 void phy_destroy(struct phy *phy);
 119 void devm_phy_destroy(struct device *dev, struct phy *phy);
 120
 121 Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
 122 associated with this PHY.
 123
 124 7. PM Runtime
 125
 126 This subsystem is pm runtime enabled. So while creating the PHY,
 127 pm_runtime_enable of the phy device created by this subsystem is called and
 128 while destroying the PHY, pm_runtime_disable is called. Note that the phy
 129 device created by this subsystem will be a child of the device that calls
 130 phy_create (PHY provider device).
 131
 132 So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
 133 pm_runtime_get_sync of PHY provider device because of parent-child relationship.
 134 It should also be noted that phy_power_on and phy_power_off performs
 135 phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
 136 There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
 137 phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
 138 phy_pm_runtime_forbid for performing PM operations.
 139
 140 8. Board File Initialization
 141
 142 Certain board file initialization is necessary in order to get a reference
 143 to the PHY in the case of non-dt boot.
 144 Say we have a single device that implements 3 PHYs that of USB, SATA and PCIe,
 145 then in the board file the following initialization should be done.
 146
 147 struct phy_consumer consumers[] = {
 148         PHY_CONSUMER("dwc3.0", "usb"),
 149         PHY_CONSUMER("pcie.0", "pcie"),
 150         PHY_CONSUMER("sata.0", "sata"),
 151 };
 152 PHY_CONSUMER takes 2 parameters, first is the device name of the controller
 153 (PHY consumer) and second is the port name.
 154
 155 struct phy_init_data init_data = {
 156         .consumers = consumers,
 157         .num_consumers = ARRAY_SIZE(consumers),
 158 };
 159
 160 static const struct platform_device pipe3_phy_dev = {
 161         .name = "pipe3-phy",
 162         .id = -1,
 163         .dev = {
 164                 .platform_data = {
 165                         .init_data = &init_data,
 166                 },
 167         },
 168 };
 169
 170 then, while doing phy_create, the PHY driver should pass this init_data
 171         phy_create(dev, ops, pdata->init_data);
 172
 173 and the controller driver (phy consumer) should pass the port name along with
 174 the device to get a reference to the PHY
 175         phy_get(dev, "pcie");
 176
 177 9. DeviceTree Binding
 178
 179 The documentation for PHY dt binding can be found @
 180 Documentation/devicetree/bindings/phy/phy-bindings.txt