Documentation/phy.txt - kernel/msm-4.19 - Gitiles

 			    PHY SUBSYSTEM
 		  Kishon Vijay Abraham I <kishon@ti.com>

 This document explains the Generic PHY Framework along with the APIs provided,
 and how-to-use.

 1. Introduction

 *PHY* is the abbreviation for physical layer. It is used to connect a device
 to the physical medium e.g., the USB controller has a PHY to provide functions
 such as serialization, de-serialization, encoding, decoding and is responsible
 for obtaining the required data transmission rate. Note that some USB
 controllers have PHY functionality embedded into it and others use an external
 PHY. Other peripherals that use PHY include Wireless LAN, Ethernet,
 SATA etc.

 The intention of creating this framework is to bring the PHY drivers spread
 all over the Linux kernel to drivers/phy to increase code re-use and for
 better code maintainability.

 This framework will be of use only to devices that use external PHY (PHY
 functionality is not embedded within the controller).

 2. Registering/Unregistering the PHY provider

 PHY provider refers to an entity that implements one or more PHY instances.
 For the simple case where the PHY provider implements only a single instance of
 the PHY, the framework provides its own implementation of of_xlate in
 of_phy_simple_xlate. If the PHY provider implements multiple instances, it
 should provide its own implementation of of_xlate. of_xlate is used only for
 dt boot case.

 #define of_phy_provider_register(dev, xlate)    \
         __of_phy_provider_register((dev), THIS_MODULE, (xlate))

 #define devm_of_phy_provider_register(dev, xlate)       \
         __devm_of_phy_provider_register((dev), THIS_MODULE, (xlate))

 of_phy_provider_register and devm_of_phy_provider_register macros can be used to
 register the phy_provider and it takes device and of_xlate as
 arguments. For the dt boot case, all PHY providers should use one of the above
 2 macros to register the PHY provider.

 void devm_of_phy_provider_unregister(struct device *dev,
 	struct phy_provider *phy_provider);
 void of_phy_provider_unregister(struct phy_provider *phy_provider);

 devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to
 unregister the PHY.

 3. Creating the PHY

 The PHY driver should create the PHY in order for other peripheral controllers
 to make use of it. The PHY framework provides 2 APIs to create the PHY.

 struct phy *phy_create(struct device *dev, const struct phy_ops *ops,
         struct phy_init_data *init_data);
 struct phy *devm_phy_create(struct device *dev, const struct phy_ops *ops,
 	struct phy_init_data *init_data);

 The PHY drivers can use one of the above 2 APIs to create the PHY by passing
 the device pointer, phy ops and init_data.
 phy_ops is a set of function pointers for performing PHY operations such as
 init, exit, power_on and power_off. *init_data* is mandatory to get a reference
 to the PHY in the case of non-dt boot. See section *Board File Initialization*
 on how init_data should be used.

 Inorder to dereference the private data (in phy_ops), the phy provider driver
 can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
 phy_ops to get back the private data.

 4. Getting a reference to the PHY

 Before the controller can make use of the PHY, it has to get a reference to
 it. This framework provides the following APIs to get a reference to the PHY.

 struct phy *phy_get(struct device *dev, const char *string);
 struct phy *devm_phy_get(struct device *dev, const char *string);

 phy_get and devm_phy_get can be used to get the PHY. In the case of dt boot,
 the string arguments should contain the phy name as given in the dt data and
 in the case of non-dt boot, it should contain the label of the PHY.
 The only difference between the two APIs is that devm_phy_get associates the
 device with the PHY using devres on successful PHY get. On driver detach,
 release function is invoked on the the devres data and devres data is freed.

 5. Releasing a reference to the PHY

 When the controller no longer needs the PHY, it has to release the reference
 to the PHY it has obtained using the APIs mentioned in the above section. The
 PHY framework provides 2 APIs to release a reference to the PHY.

 void phy_put(struct phy *phy);
 void devm_phy_put(struct device *dev, struct phy *phy);

 Both these APIs are used to release a reference to the PHY and devm_phy_put
 destroys the devres associated with this PHY.

 6. Destroying the PHY

 When the driver that created the PHY is unloaded, it should destroy the PHY it
 created using one of the following 2 APIs.

 void phy_destroy(struct phy *phy);
 void devm_phy_destroy(struct device *dev, struct phy *phy);

 Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
 associated with this PHY.

 7. PM Runtime

 This subsystem is pm runtime enabled. So while creating the PHY,
 pm_runtime_enable of the phy device created by this subsystem is called and
 while destroying the PHY, pm_runtime_disable is called. Note that the phy
 device created by this subsystem will be a child of the device that calls
 phy_create (PHY provider device).

 So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
 pm_runtime_get_sync of PHY provider device because of parent-child relationship.
 It should also be noted that phy_power_on and phy_power_off performs
 phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
 There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
 phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
 phy_pm_runtime_forbid for performing PM operations.

 8. Board File Initialization

 Certain board file initialization is necessary in order to get a reference
 to the PHY in the case of non-dt boot.
 Say we have a single device that implements 3 PHYs that of USB, SATA and PCIe,
 then in the board file the following initialization should be done.

 struct phy_consumer consumers[] = {
 	PHY_CONSUMER("dwc3.0", "usb"),
 	PHY_CONSUMER("pcie.0", "pcie"),
 	PHY_CONSUMER("sata.0", "sata"),
 };
 PHY_CONSUMER takes 2 parameters, first is the device name of the controller
 (PHY consumer) and second is the port name.

 struct phy_init_data init_data = {
 	.consumers = consumers,
 	.num_consumers = ARRAY_SIZE(consumers),
 };

 static const struct platform_device pipe3_phy_dev = {
 	.name = "pipe3-phy",
 	.id = -1,
 	.dev = {
 		.platform_data = {
 			.init_data = &init_data,
 		},
 	},
 };

 then, while doing phy_create, the PHY driver should pass this init_data
 	phy_create(dev, ops, pdata->init_data);

 and the controller driver (phy consumer) should pass the port name along with
 the device to get a reference to the PHY
 	phy_get(dev, "pcie");

 9. DeviceTree Binding

 The documentation for PHY dt binding can be found @
 Documentation/devicetree/bindings/phy/phy-bindings.txt
	PHY SUBSYSTEM
	Kishon Vijay Abraham I <kishon@ti.com>

	This document explains the Generic PHY Framework along with the APIs provided,
	and how-to-use.

	1. Introduction

	PHY is the abbreviation for physical layer. It is used to connect a device
	to the physical medium e.g., the USB controller has a PHY to provide functions
	such as serialization, de-serialization, encoding, decoding and is responsible
	for obtaining the required data transmission rate. Note that some USB
	controllers have PHY functionality embedded into it and others use an external
	PHY. Other peripherals that use PHY include Wireless LAN, Ethernet,
	SATA etc.

	The intention of creating this framework is to bring the PHY drivers spread
	all over the Linux kernel to drivers/phy to increase code re-use and for
	better code maintainability.

	This framework will be of use only to devices that use external PHY (PHY
	functionality is not embedded within the controller).

	2. Registering/Unregistering the PHY provider

	PHY provider refers to an entity that implements one or more PHY instances.
	For the simple case where the PHY provider implements only a single instance of
	the PHY, the framework provides its own implementation of of_xlate in
	of_phy_simple_xlate. If the PHY provider implements multiple instances, it
	should provide its own implementation of of_xlate. of_xlate is used only for
	dt boot case.

	#define of_phy_provider_register(dev, xlate) \
	__of_phy_provider_register((dev), THIS_MODULE, (xlate))

	#define devm_of_phy_provider_register(dev, xlate) \
	__devm_of_phy_provider_register((dev), THIS_MODULE, (xlate))

	of_phy_provider_register and devm_of_phy_provider_register macros can be used to
	register the phy_provider and it takes device and of_xlate as
	arguments. For the dt boot case, all PHY providers should use one of the above
	2 macros to register the PHY provider.

	void devm_of_phy_provider_unregister(struct device *dev,
	struct phy_provider *phy_provider);
	void of_phy_provider_unregister(struct phy_provider *phy_provider);

	devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to
	unregister the PHY.

	3. Creating the PHY

	The PHY driver should create the PHY in order for other peripheral controllers
	to make use of it. The PHY framework provides 2 APIs to create the PHY.

	struct phy phy_create(struct device dev, const struct phy_ops *ops,
	struct phy_init_data *init_data);
	struct phy devm_phy_create(struct device dev, const struct phy_ops *ops,
	struct phy_init_data *init_data);

	The PHY drivers can use one of the above 2 APIs to create the PHY by passing
	the device pointer, phy ops and init_data.
	phy_ops is a set of function pointers for performing PHY operations such as
	init, exit, power_on and power_off. init_data is mandatory to get a reference
	to the PHY in the case of non-dt boot. See section Board File Initialization
	on how init_data should be used.

	Inorder to dereference the private data (in phy_ops), the phy provider driver
	can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
	phy_ops to get back the private data.

	4. Getting a reference to the PHY

	Before the controller can make use of the PHY, it has to get a reference to
	it. This framework provides the following APIs to get a reference to the PHY.

	struct phy phy_get(struct device dev, const char *string);
	struct phy devm_phy_get(struct device dev, const char *string);

	phy_get and devm_phy_get can be used to get the PHY. In the case of dt boot,
	the string arguments should contain the phy name as given in the dt data and
	in the case of non-dt boot, it should contain the label of the PHY.
	The only difference between the two APIs is that devm_phy_get associates the
	device with the PHY using devres on successful PHY get. On driver detach,
	release function is invoked on the the devres data and devres data is freed.

	5. Releasing a reference to the PHY

	When the controller no longer needs the PHY, it has to release the reference
	to the PHY it has obtained using the APIs mentioned in the above section. The
	PHY framework provides 2 APIs to release a reference to the PHY.

	void phy_put(struct phy *phy);
	void devm_phy_put(struct device dev, struct phy phy);

	Both these APIs are used to release a reference to the PHY and devm_phy_put
	destroys the devres associated with this PHY.

	6. Destroying the PHY

	When the driver that created the PHY is unloaded, it should destroy the PHY it
	created using one of the following 2 APIs.

	void phy_destroy(struct phy *phy);
	void devm_phy_destroy(struct device dev, struct phy phy);

	Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
	associated with this PHY.

	7. PM Runtime

	This subsystem is pm runtime enabled. So while creating the PHY,
	pm_runtime_enable of the phy device created by this subsystem is called and
	while destroying the PHY, pm_runtime_disable is called. Note that the phy
	device created by this subsystem will be a child of the device that calls
	phy_create (PHY provider device).

	So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
	pm_runtime_get_sync of PHY provider device because of parent-child relationship.
	It should also be noted that phy_power_on and phy_power_off performs
	phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
	There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
	phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
	phy_pm_runtime_forbid for performing PM operations.

	8. Board File Initialization

	Certain board file initialization is necessary in order to get a reference
	to the PHY in the case of non-dt boot.
	Say we have a single device that implements 3 PHYs that of USB, SATA and PCIe,
	then in the board file the following initialization should be done.

	struct phy_consumer consumers[] = {
	PHY_CONSUMER("dwc3.0", "usb"),
	PHY_CONSUMER("pcie.0", "pcie"),
	PHY_CONSUMER("sata.0", "sata"),
	};
	PHY_CONSUMER takes 2 parameters, first is the device name of the controller
	(PHY consumer) and second is the port name.

	struct phy_init_data init_data = {
	.consumers = consumers,
	.num_consumers = ARRAY_SIZE(consumers),
	};

	static const struct platform_device pipe3_phy_dev = {
	.name = "pipe3-phy",
	.id = -1,
	.dev = {
	.platform_data = {
	.init_data = &init_data,
	},
	},
	};

	then, while doing phy_create, the PHY driver should pass this init_data
	phy_create(dev, ops, pdata->init_data);

	and the controller driver (phy consumer) should pass the port name along with
	the device to get a reference to the PHY
	phy_get(dev, "pcie");

	9. DeviceTree Binding

	The documentation for PHY dt binding can be found @
	Documentation/devicetree/bindings/phy/phy-bindings.txt