About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / phy.txt




Custom Search

Based on kernel version 4.1. Page generated on 2015-06-28 12:13 EST.

1				    PHY SUBSYSTEM
2			  Kishon Vijay Abraham I <kishon@ti.com>
3	
4	This document explains the Generic PHY Framework along with the APIs provided,
5	and how-to-use.
6	
7	1. Introduction
8	
9	*PHY* is the abbreviation for physical layer. It is used to connect a device
10	to the physical medium e.g., the USB controller has a PHY to provide functions
11	such as serialization, de-serialization, encoding, decoding and is responsible
12	for obtaining the required data transmission rate. Note that some USB
13	controllers have PHY functionality embedded into it and others use an external
14	PHY. Other peripherals that use PHY include Wireless LAN, Ethernet,
15	SATA etc.
16	
17	The intention of creating this framework is to bring the PHY drivers spread
18	all over the Linux kernel to drivers/phy to increase code re-use and for
19	better code maintainability.
20	
21	This framework will be of use only to devices that use external PHY (PHY
22	functionality is not embedded within the controller).
23	
24	2. Registering/Unregistering the PHY provider
25	
26	PHY provider refers to an entity that implements one or more PHY instances.
27	For the simple case where the PHY provider implements only a single instance of
28	the PHY, the framework provides its own implementation of of_xlate in
29	of_phy_simple_xlate. If the PHY provider implements multiple instances, it
30	should provide its own implementation of of_xlate. of_xlate is used only for
31	dt 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	
39	of_phy_provider_register and devm_of_phy_provider_register macros can be used to
40	register the phy_provider and it takes device and of_xlate as
41	arguments. For the dt boot case, all PHY providers should use one of the above
42	2 macros to register the PHY provider.
43	
44	void devm_of_phy_provider_unregister(struct device *dev,
45		struct phy_provider *phy_provider);
46	void of_phy_provider_unregister(struct phy_provider *phy_provider);
47	
48	devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to
49	unregister the PHY.
50	
51	3. Creating the PHY
52	
53	The PHY driver should create the PHY in order for other peripheral controllers
54	to make use of it. The PHY framework provides 2 APIs to create the PHY.
55	
56	struct phy *phy_create(struct device *dev, struct device_node *node,
57			       const struct phy_ops *ops);
58	struct phy *devm_phy_create(struct device *dev, struct device_node *node,
59				    const struct phy_ops *ops);
60	
61	The PHY drivers can use one of the above 2 APIs to create the PHY by passing
62	the device pointer and phy ops.
63	phy_ops is a set of function pointers for performing PHY operations such as
64	init, exit, power_on and power_off.
65	
66	Inorder to dereference the private data (in phy_ops), the phy provider driver
67	can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
68	phy_ops to get back the private data.
69	
70	4. Getting a reference to the PHY
71	
72	Before the controller can make use of the PHY, it has to get a reference to
73	it. This framework provides the following APIs to get a reference to the PHY.
74	
75	struct phy *phy_get(struct device *dev, const char *string);
76	struct phy *phy_optional_get(struct device *dev, const char *string);
77	struct phy *devm_phy_get(struct device *dev, const char *string);
78	struct phy *devm_phy_optional_get(struct device *dev, const char *string);
79	
80	phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can
81	be used to get the PHY. In the case of dt boot, the string arguments
82	should contain the phy name as given in the dt data and in the case of
83	non-dt boot, it should contain the label of the PHY.  The two
84	devm_phy_get associates the device with the PHY using devres on
85	successful PHY get. On driver detach, release function is invoked on
86	the the devres data and devres data is freed. phy_optional_get and
87	devm_phy_optional_get should be used when the phy is optional. These
88	two functions will never return -ENODEV, but instead returns NULL when
89	the phy cannot be found.
90	
91	It should be noted that NULL is a valid phy reference. All phy
92	consumer calls on the NULL phy become NOPs. That is the release calls,
93	the phy_init() and phy_exit() calls, and phy_power_on() and
94	phy_power_off() calls are all NOP when applied to a NULL phy. The NULL
95	phy is useful in devices for handling optional phy devices.
96	
97	5. Releasing a reference to the PHY
98	
99	When the controller no longer needs the PHY, it has to release the reference
100	to the PHY it has obtained using the APIs mentioned in the above section. The
101	PHY framework provides 2 APIs to release a reference to the PHY.
102	
103	void phy_put(struct phy *phy);
104	void devm_phy_put(struct device *dev, struct phy *phy);
105	
106	Both these APIs are used to release a reference to the PHY and devm_phy_put
107	destroys the devres associated with this PHY.
108	
109	6. Destroying the PHY
110	
111	When the driver that created the PHY is unloaded, it should destroy the PHY it
112	created using one of the following 2 APIs.
113	
114	void phy_destroy(struct phy *phy);
115	void devm_phy_destroy(struct device *dev, struct phy *phy);
116	
117	Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
118	associated with this PHY.
119	
120	7. PM Runtime
121	
122	This subsystem is pm runtime enabled. So while creating the PHY,
123	pm_runtime_enable of the phy device created by this subsystem is called and
124	while destroying the PHY, pm_runtime_disable is called. Note that the phy
125	device created by this subsystem will be a child of the device that calls
126	phy_create (PHY provider device).
127	
128	So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
129	pm_runtime_get_sync of PHY provider device because of parent-child relationship.
130	It should also be noted that phy_power_on and phy_power_off performs
131	phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
132	There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
133	phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
134	phy_pm_runtime_forbid for performing PM operations.
135	
136	8. PHY Mappings
137	
138	In order to get reference to a PHY without help from DeviceTree, the framework
139	offers lookups which can be compared to clkdev that allow clk structures to be
140	bound to devices. A lookup can be made be made during runtime when a handle to
141	the struct phy already exists.
142	
143	The framework offers the following API for registering and unregistering the
144	lookups.
145	
146	int phy_create_lookup(struct phy *phy, const char *con_id, const char *dev_id);
147	void phy_remove_lookup(struct phy *phy, const char *con_id, const char *dev_id);
148	
149	9. DeviceTree Binding
150	
151	The documentation for PHY dt binding can be found @
152	Documentation/devicetree/bindings/phy/phy-bindings.txt
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.