1============= 2PHY subsystem 3============= 4 5:Author: Kishon Vijay Abraham I <kishon@ti.com> 6 7This document explains the Generic PHY Framework along with the APIs provided, 8and how-to-use. 9 10Introduction 11============ 12 13*PHY* is the abbreviation for physical layer. It is used to connect a device 14to the physical medium e.g., the USB controller has a PHY to provide functions 15such as serialization, de-serialization, encoding, decoding and is responsible 16for obtaining the required data transmission rate. Note that some USB 17controllers have PHY functionality embedded into it and others use an external 18PHY. Other peripherals that use PHY include Wireless LAN, Ethernet, 19SATA etc. 20 21The intention of creating this framework is to bring the PHY drivers spread 22all over the Linux kernel to drivers/phy to increase code re-use and for 23better code maintainability. 24 25This framework will be of use only to devices that use external PHY (PHY 26functionality is not embedded within the controller). 27 28Registering/Unregistering the PHY provider 29========================================== 30 31PHY provider refers to an entity that implements one or more PHY instances. 32For the simple case where the PHY provider implements only a single instance of 33the PHY, the framework provides its own implementation of of_xlate in 34of_phy_simple_xlate. If the PHY provider implements multiple instances, it 35should provide its own implementation of of_xlate. of_xlate is used only for 36dt boot case. 37 38:: 39 40 #define of_phy_provider_register(dev, xlate) \ 41 __of_phy_provider_register((dev), NULL, THIS_MODULE, (xlate)) 42 43 #define devm_of_phy_provider_register(dev, xlate) \ 44 __devm_of_phy_provider_register((dev), NULL, THIS_MODULE, 45 (xlate)) 46 47of_phy_provider_register and devm_of_phy_provider_register macros can be used to 48register the phy_provider and it takes device and of_xlate as 49arguments. For the dt boot case, all PHY providers should use one of the above 502 macros to register the PHY provider. 51 52Often the device tree nodes associated with a PHY provider will contain a set 53of children that each represent a single PHY. Some bindings may nest the child 54nodes within extra levels for context and extensibility, in which case the low 55level of_phy_provider_register_full() and devm_of_phy_provider_register_full() 56macros can be used to override the node containing the children. 57 58:: 59 60 #define of_phy_provider_register_full(dev, children, xlate) \ 61 __of_phy_provider_register(dev, children, THIS_MODULE, xlate) 62 63 #define devm_of_phy_provider_register_full(dev, children, xlate) \ 64 __devm_of_phy_provider_register_full(dev, children, 65 THIS_MODULE, xlate) 66 67 void devm_of_phy_provider_unregister(struct device *dev, 68 struct phy_provider *phy_provider); 69 void of_phy_provider_unregister(struct phy_provider *phy_provider); 70 71devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to 72unregister the PHY. 73 74Creating the PHY 75================ 76 77The PHY driver should create the PHY in order for other peripheral controllers 78to make use of it. The PHY framework provides 2 APIs to create the PHY. 79 80:: 81 82 struct phy *phy_create(struct device *dev, struct device_node *node, 83 const struct phy_ops *ops); 84 struct phy *devm_phy_create(struct device *dev, 85 struct device_node *node, 86 const struct phy_ops *ops); 87 88The PHY drivers can use one of the above 2 APIs to create the PHY by passing 89the device pointer and phy ops. 90phy_ops is a set of function pointers for performing PHY operations such as 91init, exit, power_on and power_off. 92 93Inorder to dereference the private data (in phy_ops), the phy provider driver 94can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in 95phy_ops to get back the private data. 96 97Getting a reference to the PHY 98============================== 99 100Before the controller can make use of the PHY, it has to get a reference to 101it. This framework provides the following APIs to get a reference to the PHY. 102 103:: 104 105 struct phy *phy_get(struct device *dev, const char *string); 106 struct phy *devm_phy_get(struct device *dev, const char *string); 107 struct phy *devm_phy_optional_get(struct device *dev, 108 const char *string); 109 struct phy *devm_of_phy_get(struct device *dev, struct device_node *np, 110 const char *con_id); 111 struct phy *devm_of_phy_optional_get(struct device *dev, 112 struct device_node *np, 113 const char *con_id); 114 struct phy *devm_of_phy_get_by_index(struct device *dev, 115 struct device_node *np, 116 int index); 117 118phy_get, devm_phy_get and devm_phy_optional_get can be used to get the PHY. 119In the case of dt boot, the string arguments 120should contain the phy name as given in the dt data and in the case of 121non-dt boot, it should contain the label of the PHY. The two 122devm_phy_get associates the device with the PHY using devres on 123successful PHY get. On driver detach, release function is invoked on 124the devres data and devres data is freed. 125The _optional_get variants should be used when the phy is optional. These 126functions will never return -ENODEV, but instead return NULL when 127the phy cannot be found. 128Some generic drivers, such as ehci, may use multiple phys. In this case, 129devm_of_phy_get or devm_of_phy_get_by_index can be used to get a phy 130reference based on name or index. 131 132It should be noted that NULL is a valid phy reference. All phy 133consumer calls on the NULL phy become NOPs. That is the release calls, 134the phy_init() and phy_exit() calls, and phy_power_on() and 135phy_power_off() calls are all NOP when applied to a NULL phy. The NULL 136phy is useful in devices for handling optional phy devices. 137 138Order of API calls 139================== 140 141The general order of calls should be:: 142 143 [devm_][of_]phy_get() 144 phy_init() 145 phy_power_on() 146 [phy_set_mode[_ext]()] 147 ... 148 phy_power_off() 149 phy_exit() 150 [[of_]phy_put()] 151 152Some PHY drivers may not implement :c:func:`phy_init` or :c:func:`phy_power_on`, 153but controllers should always call these functions to be compatible with other 154PHYs. Some PHYs may require :c:func:`phy_set_mode <phy_set_mode_ext>`, while 155others may use a default mode (typically configured via devicetree or other 156firmware). For compatibility, you should always call this function if you know 157what mode you will be using. Generally, this function should be called after 158:c:func:`phy_power_on`, although some PHY drivers may allow it at any time. 159 160Releasing a reference to the PHY 161================================ 162 163When the controller no longer needs the PHY, it has to release the reference 164to the PHY it has obtained using the APIs mentioned in the above section. The 165PHY framework provides 2 APIs to release a reference to the PHY. 166 167:: 168 169 void phy_put(struct phy *phy); 170 void devm_phy_put(struct device *dev, struct phy *phy); 171 172Both these APIs are used to release a reference to the PHY and devm_phy_put 173destroys the devres associated with this PHY. 174 175Destroying the PHY 176================== 177 178When the driver that created the PHY is unloaded, it should destroy the PHY it 179created using one of the following 2 APIs:: 180 181 void phy_destroy(struct phy *phy); 182 void devm_phy_destroy(struct device *dev, struct phy *phy); 183 184Both these APIs destroy the PHY and devm_phy_destroy destroys the devres 185associated with this PHY. 186 187PM Runtime 188========== 189 190This subsystem is pm runtime enabled. So while creating the PHY, 191pm_runtime_enable of the phy device created by this subsystem is called and 192while destroying the PHY, pm_runtime_disable is called. Note that the phy 193device created by this subsystem will be a child of the device that calls 194phy_create (PHY provider device). 195 196So pm_runtime_get_sync of the phy_device created by this subsystem will invoke 197pm_runtime_get_sync of PHY provider device because of parent-child relationship. 198It should also be noted that phy_power_on and phy_power_off performs 199phy_pm_runtime_get_sync and phy_pm_runtime_put respectively. 200There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync, 201phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and 202phy_pm_runtime_forbid for performing PM operations. 203 204PHY Mappings 205============ 206 207In order to get reference to a PHY without help from DeviceTree, the framework 208offers lookups which can be compared to clkdev that allow clk structures to be 209bound to devices. A lookup can be made during runtime when a handle to the 210struct phy already exists. 211 212The framework offers the following API for registering and unregistering the 213lookups:: 214 215 int phy_create_lookup(struct phy *phy, const char *con_id, 216 const char *dev_id); 217 void phy_remove_lookup(struct phy *phy, const char *con_id, 218 const char *dev_id); 219 220DeviceTree Binding 221================== 222 223The documentation for PHY dt binding can be found @ 224Documentation/devicetree/bindings/phy/phy-bindings.txt 225