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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 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, const struct phy_ops *ops,
57	        struct phy_init_data *init_data);
58	struct phy *devm_phy_create(struct device *dev, const struct phy_ops *ops,
59		struct phy_init_data *init_data);
60	
61	The PHY drivers can use one of the above 2 APIs to create the PHY by passing
62	the device pointer, phy ops and init_data.
63	phy_ops is a set of function pointers for performing PHY operations such as
64	init, exit, power_on and power_off. *init_data* is mandatory to get a reference
65	to the PHY in the case of non-dt boot. See section *Board File Initialization*
66	on how init_data should be used.
67	
68	Inorder to dereference the private data (in phy_ops), the phy provider driver
69	can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
70	phy_ops to get back the private data.
71	
72	4. Getting a reference to the PHY
73	
74	Before the controller can make use of the PHY, it has to get a reference to
75	it. This framework provides the following APIs to get a reference to the PHY.
76	
77	struct phy *phy_get(struct device *dev, const char *string);
78	struct phy *devm_phy_get(struct device *dev, const char *string);
79	
80	phy_get and devm_phy_get can be used to get the PHY. In the case of dt boot,
81	the string arguments should contain the phy name as given in the dt data and
82	in the case of non-dt boot, it should contain the label of the PHY.
83	The only difference between the two APIs is that devm_phy_get associates the
84	device with the PHY using devres on successful PHY get. On driver detach,
85	release function is invoked on the the devres data and devres data is freed.
86	
87	5. Releasing a reference to the PHY
88	
89	When the controller no longer needs the PHY, it has to release the reference
90	to the PHY it has obtained using the APIs mentioned in the above section. The
91	PHY framework provides 2 APIs to release a reference to the PHY.
92	
93	void phy_put(struct phy *phy);
94	void devm_phy_put(struct device *dev, struct phy *phy);
95	
96	Both these APIs are used to release a reference to the PHY and devm_phy_put
97	destroys the devres associated with this PHY.
98	
99	6. Destroying the PHY
100	
101	When the driver that created the PHY is unloaded, it should destroy the PHY it
102	created using one of the following 2 APIs.
103	
104	void phy_destroy(struct phy *phy);
105	void devm_phy_destroy(struct device *dev, struct phy *phy);
106	
107	Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
108	associated with this PHY.
109	
110	7. PM Runtime
111	
112	This subsystem is pm runtime enabled. So while creating the PHY,
113	pm_runtime_enable of the phy device created by this subsystem is called and
114	while destroying the PHY, pm_runtime_disable is called. Note that the phy
115	device created by this subsystem will be a child of the device that calls
116	phy_create (PHY provider device).
117	
118	So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
119	pm_runtime_get_sync of PHY provider device because of parent-child relationship.
120	It should also be noted that phy_power_on and phy_power_off performs
121	phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
122	There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
123	phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
124	phy_pm_runtime_forbid for performing PM operations.
125	
126	8. Board File Initialization
127	
128	Certain board file initialization is necessary in order to get a reference
129	to the PHY in the case of non-dt boot.
130	Say we have a single device that implements 3 PHYs that of USB, SATA and PCIe,
131	then in the board file the following initialization should be done.
132	
133	struct phy_consumer consumers[] = {
134		PHY_CONSUMER("dwc3.0", "usb"),
135		PHY_CONSUMER("pcie.0", "pcie"),
136		PHY_CONSUMER("sata.0", "sata"),
137	};
138	PHY_CONSUMER takes 2 parameters, first is the device name of the controller
139	(PHY consumer) and second is the port name.
140	
141	struct phy_init_data init_data = {
142		.consumers = consumers,
143		.num_consumers = ARRAY_SIZE(consumers),
144	};
145	
146	static const struct platform_device pipe3_phy_dev = {
147		.name = "pipe3-phy",
148		.id = -1,
149		.dev = {
150			.platform_data = {
151				.init_data = &init_data,
152			},
153		},
154	};
155	
156	then, while doing phy_create, the PHY driver should pass this init_data
157		phy_create(dev, ops, pdata->init_data);
158	
159	and the controller driver (phy consumer) should pass the port name along with
160	the device to get a reference to the PHY
161		phy_get(dev, "pcie");
162	
163	9. DeviceTree Binding
164	
165	The documentation for PHY dt binding can be found @
166	Documentation/devicetree/bindings/phy/phy-bindings.txt
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