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Based on kernel version 3.16. Page generated on 2014-08-06 21:40 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 *phy_optional_get(struct device *dev, const char *string);
79	struct phy *devm_phy_get(struct device *dev, const char *string);
80	struct phy *devm_phy_optional_get(struct device *dev, const char *string);
81	
82	phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can
83	be used to get the PHY. In the case of dt boot, the string arguments
84	should contain the phy name as given in the dt data and in the case of
85	non-dt boot, it should contain the label of the PHY.  The two
86	devm_phy_get associates the device with the PHY using devres on
87	successful PHY get. On driver detach, release function is invoked on
88	the the devres data and devres data is freed. phy_optional_get and
89	devm_phy_optional_get should be used when the phy is optional. These
90	two functions will never return -ENODEV, but instead returns NULL when
91	the phy cannot be found.
92	
93	It should be noted that NULL is a valid phy reference. All phy
94	consumer calls on the NULL phy become NOPs. That is the release calls,
95	the phy_init() and phy_exit() calls, and phy_power_on() and
96	phy_power_off() calls are all NOP when applied to a NULL phy. The NULL
97	phy is useful in devices for handling optional phy devices.
98	
99	5. Releasing a reference to the PHY
100	
101	When the controller no longer needs the PHY, it has to release the reference
102	to the PHY it has obtained using the APIs mentioned in the above section. The
103	PHY framework provides 2 APIs to release a reference to the PHY.
104	
105	void phy_put(struct phy *phy);
106	void devm_phy_put(struct device *dev, struct phy *phy);
107	
108	Both these APIs are used to release a reference to the PHY and devm_phy_put
109	destroys the devres associated with this PHY.
110	
111	6. Destroying the PHY
112	
113	When the driver that created the PHY is unloaded, it should destroy the PHY it
114	created using one of the following 2 APIs.
115	
116	void phy_destroy(struct phy *phy);
117	void devm_phy_destroy(struct device *dev, struct phy *phy);
118	
119	Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
120	associated with this PHY.
121	
122	7. PM Runtime
123	
124	This subsystem is pm runtime enabled. So while creating the PHY,
125	pm_runtime_enable of the phy device created by this subsystem is called and
126	while destroying the PHY, pm_runtime_disable is called. Note that the phy
127	device created by this subsystem will be a child of the device that calls
128	phy_create (PHY provider device).
129	
130	So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
131	pm_runtime_get_sync of PHY provider device because of parent-child relationship.
132	It should also be noted that phy_power_on and phy_power_off performs
133	phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
134	There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
135	phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
136	phy_pm_runtime_forbid for performing PM operations.
137	
138	8. Board File Initialization
139	
140	Certain board file initialization is necessary in order to get a reference
141	to the PHY in the case of non-dt boot.
142	Say we have a single device that implements 3 PHYs that of USB, SATA and PCIe,
143	then in the board file the following initialization should be done.
144	
145	struct phy_consumer consumers[] = {
146		PHY_CONSUMER("dwc3.0", "usb"),
147		PHY_CONSUMER("pcie.0", "pcie"),
148		PHY_CONSUMER("sata.0", "sata"),
149	};
150	PHY_CONSUMER takes 2 parameters, first is the device name of the controller
151	(PHY consumer) and second is the port name.
152	
153	struct phy_init_data init_data = {
154		.consumers = consumers,
155		.num_consumers = ARRAY_SIZE(consumers),
156	};
157	
158	static const struct platform_device pipe3_phy_dev = {
159		.name = "pipe3-phy",
160		.id = -1,
161		.dev = {
162			.platform_data = {
163				.init_data = &init_data,
164			},
165		},
166	};
167	
168	then, while doing phy_create, the PHY driver should pass this init_data
169		phy_create(dev, ops, pdata->init_data);
170	
171	and the controller driver (phy consumer) should pass the port name along with
172	the device to get a reference to the PHY
173		phy_get(dev, "pcie");
174	
175	9. DeviceTree Binding
176	
177	The documentation for PHY dt binding can be found @
178	Documentation/devicetree/bindings/phy/phy-bindings.txt
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