Root/Documentation/phy.txt

1                PHY SUBSYSTEM
2          Kishon Vijay Abraham I <kishon@ti.com>
3
4This document explains the Generic PHY Framework along with the APIs provided,
5and how-to-use.
6
71. Introduction
8
9*PHY* is the abbreviation for physical layer. It is used to connect a device
10to the physical medium e.g., the USB controller has a PHY to provide functions
11such as serialization, de-serialization, encoding, decoding and is responsible
12for obtaining the required data transmission rate. Note that some USB
13controllers have PHY functionality embedded into it and others use an external
14PHY. Other peripherals that use PHY include Wireless LAN, Ethernet,
15SATA etc.
16
17The intention of creating this framework is to bring the PHY drivers spread
18all over the Linux kernel to drivers/phy to increase code re-use and for
19better code maintainability.
20
21This framework will be of use only to devices that use external PHY (PHY
22functionality is not embedded within the controller).
23
242. Registering/Unregistering the PHY provider
25
26PHY provider refers to an entity that implements one or more PHY instances.
27For the simple case where the PHY provider implements only a single instance of
28the PHY, the framework provides its own implementation of of_xlate in
29of_phy_simple_xlate. If the PHY provider implements multiple instances, it
30should provide its own implementation of of_xlate. of_xlate is used only for
31dt 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
39of_phy_provider_register and devm_of_phy_provider_register macros can be used to
40register the phy_provider and it takes device and of_xlate as
41arguments. For the dt boot case, all PHY providers should use one of the above
422 macros to register the PHY provider.
43
44void devm_of_phy_provider_unregister(struct device *dev,
45    struct phy_provider *phy_provider);
46void of_phy_provider_unregister(struct phy_provider *phy_provider);
47
48devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to
49unregister the PHY.
50
513. Creating the PHY
52
53The PHY driver should create the PHY in order for other peripheral controllers
54to make use of it. The PHY framework provides 2 APIs to create the PHY.
55
56struct phy *phy_create(struct device *dev, const struct phy_ops *ops,
57        struct phy_init_data *init_data);
58struct phy *devm_phy_create(struct device *dev, const struct phy_ops *ops,
59    struct phy_init_data *init_data);
60
61The PHY drivers can use one of the above 2 APIs to create the PHY by passing
62the device pointer, phy ops and init_data.
63phy_ops is a set of function pointers for performing PHY operations such as
64init, exit, power_on and power_off. *init_data* is mandatory to get a reference
65to the PHY in the case of non-dt boot. See section *Board File Initialization*
66on how init_data should be used.
67
68Inorder to dereference the private data (in phy_ops), the phy provider driver
69can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
70phy_ops to get back the private data.
71
724. Getting a reference to the PHY
73
74Before the controller can make use of the PHY, it has to get a reference to
75it. This framework provides the following APIs to get a reference to the PHY.
76
77struct phy *phy_get(struct device *dev, const char *string);
78struct phy *devm_phy_get(struct device *dev, const char *string);
79
80phy_get and devm_phy_get can be used to get the PHY. In the case of dt boot,
81the string arguments should contain the phy name as given in the dt data and
82in the case of non-dt boot, it should contain the label of the PHY.
83The only difference between the two APIs is that devm_phy_get associates the
84device with the PHY using devres on successful PHY get. On driver detach,
85release function is invoked on the the devres data and devres data is freed.
86
875. Releasing a reference to the PHY
88
89When the controller no longer needs the PHY, it has to release the reference
90to the PHY it has obtained using the APIs mentioned in the above section. The
91PHY framework provides 2 APIs to release a reference to the PHY.
92
93void phy_put(struct phy *phy);
94void devm_phy_put(struct device *dev, struct phy *phy);
95
96Both these APIs are used to release a reference to the PHY and devm_phy_put
97destroys the devres associated with this PHY.
98
996. Destroying the PHY
100
101When the driver that created the PHY is unloaded, it should destroy the PHY it
102created using one of the following 2 APIs.
103
104void phy_destroy(struct phy *phy);
105void devm_phy_destroy(struct device *dev, struct phy *phy);
106
107Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
108associated with this PHY.
109
1107. PM Runtime
111
112This subsystem is pm runtime enabled. So while creating the PHY,
113pm_runtime_enable of the phy device created by this subsystem is called and
114while destroying the PHY, pm_runtime_disable is called. Note that the phy
115device created by this subsystem will be a child of the device that calls
116phy_create (PHY provider device).
117
118So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
119pm_runtime_get_sync of PHY provider device because of parent-child relationship.
120It should also be noted that phy_power_on and phy_power_off performs
121phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
122There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
123phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and
124phy_pm_runtime_forbid for performing PM operations.
125
1268. Board File Initialization
127
128Certain board file initialization is necessary in order to get a reference
129to the PHY in the case of non-dt boot.
130Say we have a single device that implements 3 PHYs that of USB, SATA and PCIe,
131then in the board file the following initialization should be done.
132
133struct phy_consumer consumers[] = {
134    PHY_CONSUMER("dwc3.0", "usb"),
135    PHY_CONSUMER("pcie.0", "pcie"),
136    PHY_CONSUMER("sata.0", "sata"),
137};
138PHY_CONSUMER takes 2 parameters, first is the device name of the controller
139(PHY consumer) and second is the port name.
140
141struct phy_init_data init_data = {
142    .consumers = consumers,
143    .num_consumers = ARRAY_SIZE(consumers),
144};
145
146static 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
156then, while doing phy_create, the PHY driver should pass this init_data
157    phy_create(dev, ops, pdata->init_data);
158
159and the controller driver (phy consumer) should pass the port name along with
160the device to get a reference to the PHY
161    phy_get(dev, "pcie");
162
1639. DeviceTree Binding
164
165The documentation for PHY dt binding can be found @
166Documentation/devicetree/bindings/phy/phy-bindings.txt
167

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