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. 96 974. Getting a reference to the PHY 98 99Before the controller can make use of the PHY, it has to get a reference to 100it. This framework provides the following APIs to get a reference to the PHY. 101 102:: 103 104 struct phy *phy_get(struct device *dev, const char *string); 105 struct phy *phy_optional_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_by_index(struct device *dev, 110 struct device_node *np, 111 int index); 112 113phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can 114be used to get the PHY. In the case of dt boot, the string arguments 115should contain the phy name as given in the dt data and in the case of 116non-dt boot, it should contain the label of the PHY. The two 117devm_phy_get associates the device with the PHY using devres on 118successful PHY get. On driver detach, release function is invoked on 119the devres data and devres data is freed. phy_optional_get and 120devm_phy_optional_get should be used when the phy is optional. These 121two functions will never return -ENODEV, but instead returns NULL when 122the phy cannot be found.Some generic drivers, such as ehci, may use multiple 123phys and for such drivers referencing phy(s) by name(s) does not make sense. In 124this case, devm_of_phy_get_by_index can be used to get a phy reference based on 125the index. 126 127It should be noted that NULL is a valid phy reference. All phy 128consumer calls on the NULL phy become NOPs. That is the release calls, 129the phy_init() and phy_exit() calls, and phy_power_on() and 130phy_power_off() calls are all NOP when applied to a NULL phy. The NULL 131phy is useful in devices for handling optional phy devices. 132 133Releasing a reference to the PHY 134================================ 135 136When the controller no longer needs the PHY, it has to release the reference 137to the PHY it has obtained using the APIs mentioned in the above section. The 138PHY framework provides 2 APIs to release a reference to the PHY. 139 140:: 141 142 void phy_put(struct phy *phy); 143 void devm_phy_put(struct device *dev, struct phy *phy); 144 145Both these APIs are used to release a reference to the PHY and devm_phy_put 146destroys the devres associated with this PHY. 147 148Destroying the PHY 149================== 150 151When the driver that created the PHY is unloaded, it should destroy the PHY it 152created using one of the following 2 APIs:: 153 154 void phy_destroy(struct phy *phy); 155 void devm_phy_destroy(struct device *dev, struct phy *phy); 156 157Both these APIs destroy the PHY and devm_phy_destroy destroys the devres 158associated with this PHY. 159 160PM Runtime 161========== 162 163This subsystem is pm runtime enabled. So while creating the PHY, 164pm_runtime_enable of the phy device created by this subsystem is called and 165while destroying the PHY, pm_runtime_disable is called. Note that the phy 166device created by this subsystem will be a child of the device that calls 167phy_create (PHY provider device). 168 169So pm_runtime_get_sync of the phy_device created by this subsystem will invoke 170pm_runtime_get_sync of PHY provider device because of parent-child relationship. 171It should also be noted that phy_power_on and phy_power_off performs 172phy_pm_runtime_get_sync and phy_pm_runtime_put respectively. 173There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync, 174phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and 175phy_pm_runtime_forbid for performing PM operations. 176 177PHY Mappings 178============ 179 180In order to get reference to a PHY without help from DeviceTree, the framework 181offers lookups which can be compared to clkdev that allow clk structures to be 182bound to devices. A lookup can be made during runtime when a handle to the 183struct phy already exists. 184 185The framework offers the following API for registering and unregistering the 186lookups:: 187 188 int phy_create_lookup(struct phy *phy, const char *con_id, 189 const char *dev_id); 190 void phy_remove_lookup(struct phy *phy, const char *con_id, 191 const char *dev_id); 192 193DeviceTree Binding 194================== 195 196The documentation for PHY dt binding can be found @ 197Documentation/devicetree/bindings/phy/phy-bindings.txt 198