1 PHY SUBSYSTEM 2 Kishon Vijay Abraham I <kishon@ti.com> 3 4This document explains the Generic PHY Framework along with the APIs provided, 5and how-to-use. 6 71. Introduction 8 9*PHY* is the abbreviation for physical layer. It is used to connect a device 10to the physical medium e.g., the USB controller has a PHY to provide functions 11such as serialization, de-serialization, encoding, decoding and is responsible 12for obtaining the required data transmission rate. Note that some USB 13controllers have PHY functionality embedded into it and others use an external 14PHY. Other peripherals that use PHY include Wireless LAN, Ethernet, 15SATA etc. 16 17The intention of creating this framework is to bring the PHY drivers spread 18all over the Linux kernel to drivers/phy to increase code re-use and for 19better code maintainability. 20 21This framework will be of use only to devices that use external PHY (PHY 22functionality is not embedded within the controller). 23 242. Registering/Unregistering the PHY provider 25 26PHY provider refers to an entity that implements one or more PHY instances. 27For the simple case where the PHY provider implements only a single instance of 28the PHY, the framework provides its own implementation of of_xlate in 29of_phy_simple_xlate. If the PHY provider implements multiple instances, it 30should provide its own implementation of of_xlate. of_xlate is used only for 31dt 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 39of_phy_provider_register and devm_of_phy_provider_register macros can be used to 40register the phy_provider and it takes device and of_xlate as 41arguments. For the dt boot case, all PHY providers should use one of the above 422 macros to register the PHY provider. 43 44void devm_of_phy_provider_unregister(struct device *dev, 45 struct phy_provider *phy_provider); 46void of_phy_provider_unregister(struct phy_provider *phy_provider); 47 48devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to 49unregister the PHY. 50 513. Creating the PHY 52 53The PHY driver should create the PHY in order for other peripheral controllers 54to make use of it. The PHY framework provides 2 APIs to create the PHY. 55 56struct phy *phy_create(struct device *dev, struct device_node *node, 57 const struct phy_ops *ops); 58struct phy *devm_phy_create(struct device *dev, struct device_node *node, 59 const struct phy_ops *ops); 60 61The PHY drivers can use one of the above 2 APIs to create the PHY by passing 62the device pointer and phy ops. 63phy_ops is a set of function pointers for performing PHY operations such as 64init, exit, power_on and power_off. 65 66Inorder to dereference the private data (in phy_ops), the phy provider driver 67can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in 68phy_ops to get back the private data. 69 704. Getting a reference to the PHY 71 72Before the controller can make use of the PHY, it has to get a reference to 73it. This framework provides the following APIs to get a reference to the PHY. 74 75struct phy *phy_get(struct device *dev, const char *string); 76struct phy *phy_optional_get(struct device *dev, const char *string); 77struct phy *devm_phy_get(struct device *dev, const char *string); 78struct phy *devm_phy_optional_get(struct device *dev, const char *string); 79 80phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can 81be used to get the PHY. In the case of dt boot, the string arguments 82should contain the phy name as given in the dt data and in the case of 83non-dt boot, it should contain the label of the PHY. The two 84devm_phy_get associates the device with the PHY using devres on 85successful PHY get. On driver detach, release function is invoked on 86the the devres data and devres data is freed. phy_optional_get and 87devm_phy_optional_get should be used when the phy is optional. These 88two functions will never return -ENODEV, but instead returns NULL when 89the phy cannot be found. 90 91It should be noted that NULL is a valid phy reference. All phy 92consumer calls on the NULL phy become NOPs. That is the release calls, 93the phy_init() and phy_exit() calls, and phy_power_on() and 94phy_power_off() calls are all NOP when applied to a NULL phy. The NULL 95phy is useful in devices for handling optional phy devices. 96 975. Releasing a reference to the PHY 98 99When the controller no longer needs the PHY, it has to release the reference 100to the PHY it has obtained using the APIs mentioned in the above section. The 101PHY framework provides 2 APIs to release a reference to the PHY. 102 103void phy_put(struct phy *phy); 104void devm_phy_put(struct device *dev, struct phy *phy); 105 106Both these APIs are used to release a reference to the PHY and devm_phy_put 107destroys the devres associated with this PHY. 108 1096. Destroying the PHY 110 111When the driver that created the PHY is unloaded, it should destroy the PHY it 112created using one of the following 2 APIs. 113 114void phy_destroy(struct phy *phy); 115void devm_phy_destroy(struct device *dev, struct phy *phy); 116 117Both these APIs destroy the PHY and devm_phy_destroy destroys the devres 118associated with this PHY. 119 1207. PM Runtime 121 122This subsystem is pm runtime enabled. So while creating the PHY, 123pm_runtime_enable of the phy device created by this subsystem is called and 124while destroying the PHY, pm_runtime_disable is called. Note that the phy 125device created by this subsystem will be a child of the device that calls 126phy_create (PHY provider device). 127 128So pm_runtime_get_sync of the phy_device created by this subsystem will invoke 129pm_runtime_get_sync of PHY provider device because of parent-child relationship. 130It should also be noted that phy_power_on and phy_power_off performs 131phy_pm_runtime_get_sync and phy_pm_runtime_put respectively. 132There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync, 133phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and 134phy_pm_runtime_forbid for performing PM operations. 135 1368. PHY Mappings 137 138In order to get reference to a PHY without help from DeviceTree, the framework 139offers lookups which can be compared to clkdev that allow clk structures to be 140bound to devices. A lookup can be made be made during runtime when a handle to 141the struct phy already exists. 142 143The framework offers the following API for registering and unregistering the 144lookups. 145 146int phy_create_lookup(struct phy *phy, const char *con_id, const char *dev_id); 147void phy_remove_lookup(struct phy *phy, const char *con_id, const char *dev_id); 148 1499. DeviceTree Binding 150 151The documentation for PHY dt binding can be found @ 152Documentation/devicetree/bindings/phy/phy-bindings.txt 153