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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:55 EST.

1	=============
2	PHY subsystem
3	=============
4	
5	:Author: Kishon Vijay Abraham I <kishon@ti.com>
6	
7	This document explains the Generic PHY Framework along with the APIs provided,
8	and how-to-use.
9	
10	Introduction
11	============
12	
13	*PHY* is the abbreviation for physical layer. It is used to connect a device
14	to the physical medium e.g., the USB controller has a PHY to provide functions
15	such as serialization, de-serialization, encoding, decoding and is responsible
16	for obtaining the required data transmission rate. Note that some USB
17	controllers have PHY functionality embedded into it and others use an external
18	PHY. Other peripherals that use PHY include Wireless LAN, Ethernet,
19	SATA etc.
20	
21	The intention of creating this framework is to bring the PHY drivers spread
22	all over the Linux kernel to drivers/phy to increase code re-use and for
23	better code maintainability.
24	
25	This framework will be of use only to devices that use external PHY (PHY
26	functionality is not embedded within the controller).
27	
28	Registering/Unregistering the PHY provider
29	==========================================
30	
31	PHY provider refers to an entity that implements one or more PHY instances.
32	For the simple case where the PHY provider implements only a single instance of
33	the PHY, the framework provides its own implementation of of_xlate in
34	of_phy_simple_xlate. If the PHY provider implements multiple instances, it
35	should provide its own implementation of of_xlate. of_xlate is used only for
36	dt 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	
47	of_phy_provider_register and devm_of_phy_provider_register macros can be used to
48	register the phy_provider and it takes device and of_xlate as
49	arguments. For the dt boot case, all PHY providers should use one of the above
50	2 macros to register the PHY provider.
51	
52	Often the device tree nodes associated with a PHY provider will contain a set
53	of children that each represent a single PHY. Some bindings may nest the child
54	nodes within extra levels for context and extensibility, in which case the low
55	level of_phy_provider_register_full() and devm_of_phy_provider_register_full()
56	macros 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	
71	devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to
72	unregister the PHY.
73	
74	Creating the PHY
75	================
76	
77	The PHY driver should create the PHY in order for other peripheral controllers
78	to 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	
88	The PHY drivers can use one of the above 2 APIs to create the PHY by passing
89	the device pointer and phy ops.
90	phy_ops is a set of function pointers for performing PHY operations such as
91	init, exit, power_on and power_off.
92	
93	Inorder to dereference the private data (in phy_ops), the phy provider driver
94	can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
95	phy_ops to get back the private data.
96	
97	4. Getting a reference to the PHY
98	
99	Before the controller can make use of the PHY, it has to get a reference to
100	it. 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	
113	phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can
114	be used to get the PHY. In the case of dt boot, the string arguments
115	should contain the phy name as given in the dt data and in the case of
116	non-dt boot, it should contain the label of the PHY.  The two
117	devm_phy_get associates the device with the PHY using devres on
118	successful PHY get. On driver detach, release function is invoked on
119	the devres data and devres data is freed. phy_optional_get and
120	devm_phy_optional_get should be used when the phy is optional. These
121	two functions will never return -ENODEV, but instead returns NULL when
122	the phy cannot be found.Some generic drivers, such as ehci, may use multiple
123	phys and for such drivers referencing phy(s) by name(s) does not make sense. In
124	this case, devm_of_phy_get_by_index can be used to get a phy reference based on
125	the index.
126	
127	It should be noted that NULL is a valid phy reference. All phy
128	consumer calls on the NULL phy become NOPs. That is the release calls,
129	the phy_init() and phy_exit() calls, and phy_power_on() and
130	phy_power_off() calls are all NOP when applied to a NULL phy. The NULL
131	phy is useful in devices for handling optional phy devices.
132	
133	Releasing a reference to the PHY
134	================================
135	
136	When the controller no longer needs the PHY, it has to release the reference
137	to the PHY it has obtained using the APIs mentioned in the above section. The
138	PHY 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	
145	Both these APIs are used to release a reference to the PHY and devm_phy_put
146	destroys the devres associated with this PHY.
147	
148	Destroying the PHY
149	==================
150	
151	When the driver that created the PHY is unloaded, it should destroy the PHY it
152	created 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	
157	Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
158	associated with this PHY.
159	
160	PM Runtime
161	==========
162	
163	This subsystem is pm runtime enabled. So while creating the PHY,
164	pm_runtime_enable of the phy device created by this subsystem is called and
165	while destroying the PHY, pm_runtime_disable is called. Note that the phy
166	device created by this subsystem will be a child of the device that calls
167	phy_create (PHY provider device).
168	
169	So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
170	pm_runtime_get_sync of PHY provider device because of parent-child relationship.
171	It should also be noted that phy_power_on and phy_power_off performs
172	phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
173	There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
174	phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
175	phy_pm_runtime_forbid for performing PM operations.
176	
177	PHY Mappings
178	============
179	
180	In order to get reference to a PHY without help from DeviceTree, the framework
181	offers lookups which can be compared to clkdev that allow clk structures to be
182	bound to devices. A lookup can be made be made during runtime when a handle to
183	the struct phy already exists.
184	
185	The framework offers the following API for registering and unregistering the
186	lookups::
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	
193	DeviceTree Binding
194	==================
195	
196	The documentation for PHY dt binding can be found @
197	Documentation/devicetree/bindings/phy/phy-bindings.txt
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