projects/linux·blob master · refs

223 lines · 8.6 KiB

1=============
2PHY subsystem
3=============
4
5:Author: Kishon Vijay Abraham I <[email protected]>
6
7This document explains the Generic PHY Framework along with the APIs provided,
8and how-to-use.
9
10Introduction
11============
12
13*PHY* is the abbreviation for physical layer. It is used to connect a device
14to the physical medium e.g., the USB controller has a PHY to provide functions
15such as serialization, de-serialization, encoding, decoding and is responsible
16for obtaining the required data transmission rate. Note that some USB
17controllers have PHY functionality embedded into it and others use an external
18PHY. Other peripherals that use PHY include Wireless LAN, Ethernet,
19SATA etc.
20
21The intention of creating this framework is to bring the PHY drivers spread
22all over the Linux kernel to drivers/phy to increase code reuse and for
23better code maintainability.
24
25This framework will be of use only to devices that use external PHY (PHY
26functionality is not embedded within the controller).
27
28Registering/Unregistering the PHY provider
29==========================================
30
31PHY provider refers to an entity that implements one or more PHY instances.
32For the simple case where the PHY provider implements only a single instance of
33the PHY, the framework provides its own implementation of of_xlate in
34of_phy_simple_xlate. If the PHY provider implements multiple instances, it
35should provide its own implementation of of_xlate. of_xlate is used only for
36dt 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
47of_phy_provider_register and devm_of_phy_provider_register macros can be used to
48register the phy_provider and it takes device and of_xlate as
49arguments. For the dt boot case, all PHY providers should use one of the above
502 macros to register the PHY provider.
51
52Often the device tree nodes associated with a PHY provider will contain a set
53of children that each represent a single PHY. Some bindings may nest the child
54nodes within extra levels for context and extensibility, in which case the low
55level of_phy_provider_register_full() and devm_of_phy_provider_register_full()
56macros 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
71devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to
72unregister the PHY.
73
74Creating the PHY
75================
76
77The PHY driver should create the PHY in order for other peripheral controllers
78to 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
88The PHY drivers can use one of the above 2 APIs to create the PHY by passing
89the device pointer and phy ops.
90phy_ops is a set of function pointers for performing PHY operations such as
91init, exit, power_on and power_off.
92
93Inorder to dereference the private data (in phy_ops), the phy provider driver
94can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in
95phy_ops to get back the private data.
96
97Getting a reference to the PHY
98==============================
99
100Before the controller can make use of the PHY, it has to get a reference to
101it. This framework provides the following APIs to get a reference to the PHY.
102
103::
104
105 struct phy *phy_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(struct device *dev, struct device_node *np,
110 const char *con_id);
111 struct phy *devm_of_phy_optional_get(struct device *dev,
112 struct device_node *np,
113 const char *con_id);
114 struct phy *devm_of_phy_get_by_index(struct device *dev,
115 struct device_node *np,
116 int index);
117
118phy_get, devm_phy_get and devm_phy_optional_get can be used to get the PHY.
119In the case of dt boot, the string arguments
120should contain the phy name as given in the dt data and in the case of
121non-dt boot, it should contain the label of the PHY. The two
122devm_phy_get associates the device with the PHY using devres on
123successful PHY get. On driver detach, release function is invoked on
124the devres data and devres data is freed.
125The _optional_get variants should be used when the phy is optional. These
126functions will never return -ENODEV, but instead return NULL when
127the phy cannot be found.
128Some generic drivers, such as ehci, may use multiple phys. In this case,
129devm_of_phy_get or devm_of_phy_get_by_index can be used to get a phy
130reference based on name or index.
131
132It should be noted that NULL is a valid phy reference. All phy
133consumer calls on the NULL phy become NOPs. That is the release calls,
134the phy_init() and phy_exit() calls, and phy_power_on() and
135phy_power_off() calls are all NOP when applied to a NULL phy. The NULL
136phy is useful in devices for handling optional phy devices.
137
138Order of API calls
139==================
140
141The general order of calls should be::
142
143 [devm_][of_]phy_get()
144 phy_init()
145 phy_power_on()
146 [phy_set_mode[_ext]()]
147 ...
148 phy_power_off()
149 phy_exit()
150 [[of_]phy_put()]
151
152Some PHY drivers may not implement :c:func:`phy_init` or :c:func:`phy_power_on`,
153but controllers should always call these functions to be compatible with other
154PHYs. Some PHYs may require :c:func:`phy_set_mode <phy_set_mode_ext>`, while
155others may use a default mode (typically configured via devicetree or other
156firmware). For compatibility, you should always call this function if you know
157what mode you will be using. Generally, this function should be called after
158:c:func:`phy_power_on`, although some PHY drivers may allow it at any time.
159
160Releasing a reference to the PHY
161================================
162
163When the controller no longer needs the PHY, it has to release the reference
164to the PHY it has obtained using the APIs mentioned in the above section. The
165PHY framework provides 2 APIs to release a reference to the PHY.
166
167::
168
169 void phy_put(struct phy *phy);
170 void devm_phy_put(struct device *dev, struct phy *phy);
171
172Both these APIs are used to release a reference to the PHY and devm_phy_put
173destroys the devres associated with this PHY.
174
175Destroying the PHY
176==================
177
178When the driver that created the PHY is unloaded, it should destroy the PHY it
179created using one of the following 2 APIs::
180
181 void phy_destroy(struct phy *phy);
182 void devm_phy_destroy(struct device *dev, struct phy *phy);
183
184Both these APIs destroy the PHY and devm_phy_destroy destroys the devres
185associated with this PHY.
186
187PM Runtime
188==========
189
190This subsystem is pm runtime enabled. So while creating the PHY,
191pm_runtime_enable of the phy device created by this subsystem is called and
192while destroying the PHY, pm_runtime_disable is called. Note that the phy
193device created by this subsystem will be a child of the device that calls
194phy_create (PHY provider device).
195
196So pm_runtime_get_sync of the phy_device created by this subsystem will invoke
197pm_runtime_get_sync of PHY provider device because of parent-child relationship.
198It should also be noted that phy_power_on and phy_power_off performs
199phy_pm_runtime_get_sync and phy_pm_runtime_put respectively.
200There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync,
201phy_pm_runtime_put and phy_pm_runtime_put_sync for performing PM operations.
202
203PHY Mappings
204============
205
206In order to get reference to a PHY without help from DeviceTree, the framework
207offers lookups which can be compared to clkdev that allow clk structures to be
208bound to devices. A lookup can be made during runtime when a handle to the
209struct phy already exists.
210
211The framework offers the following API for registering and unregistering the
212lookups::
213
214 int phy_create_lookup(struct phy *phy, const char *con_id,
215 const char *dev_id);
216 void phy_remove_lookup(struct phy *phy, const char *con_id,
217 const char *dev_id);
218
219DeviceTree Binding
220==================
221
222The documentation for PHY dt binding can be found @
223Documentation/devicetree/bindings/phy/phy-bindings.txt