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Based on kernel version 3.16. Page generated on 2014-08-06 21:39 EST.

1	The Linux Hardware Monitoring kernel API.
2	=========================================
3	
4	Guenter Roeck
5	
6	Introduction
7	------------
8	
9	This document describes the API that can be used by hardware monitoring
10	drivers that want to use the hardware monitoring framework.
11	
12	This document does not describe what a hardware monitoring (hwmon) Driver or
13	Device is. It also does not describe the API which can be used by user space
14	to communicate with a hardware monitoring device. If you want to know this
15	then please read the following file: Documentation/hwmon/sysfs-interface.
16	
17	For additional guidelines on how to write and improve hwmon drivers, please
18	also read Documentation/hwmon/submitting-patches.
19	
20	The API
21	-------
22	Each hardware monitoring driver must #include <linux/hwmon.h> and, in most
23	cases, <linux/hwmon-sysfs.h>. linux/hwmon.h declares the following
24	register/unregister functions:
25	
26	struct device *hwmon_device_register(struct device *dev);
27	struct device *
28	hwmon_device_register_with_groups(struct device *dev, const char *name,
29					  void *drvdata,
30					  const struct attribute_group **groups);
31	
32	struct device *
33	devm_hwmon_device_register_with_groups(struct device *dev,
34					       const char *name, void *drvdata,
35					       const struct attribute_group **groups);
36	
37	void hwmon_device_unregister(struct device *dev);
38	void devm_hwmon_device_unregister(struct device *dev);
39	
40	hwmon_device_register registers a hardware monitoring device. The parameter
41	of this function is a pointer to the parent device.
42	This function returns a pointer to the newly created hardware monitoring device
43	or PTR_ERR for failure. If this registration function is used, hardware
44	monitoring sysfs attributes are expected to have been created and attached to
45	the parent device prior to calling hwmon_device_register. A name attribute must
46	have been created by the caller.
47	
48	hwmon_device_register_with_groups is similar to hwmon_device_register. However,
49	it has additional parameters. The name parameter is a pointer to the hwmon
50	device name. The registration function wil create a name sysfs attribute
51	pointing to this name. The drvdata parameter is the pointer to the local
52	driver data.  hwmon_device_register_with_groups will attach this pointer
53	to the newly allocated hwmon device. The pointer can be retrieved by the driver
54	using dev_get_drvdata() on the hwmon device pointer. The groups parameter is
55	a pointer to a list of sysfs attribute groups. The list must be NULL terminated.
56	hwmon_device_register_with_groups creates the hwmon device with name attribute
57	as well as all sysfs attributes attached to the hwmon device.
58	
59	devm_hwmon_device_register_with_groups is similar to
60	hwmon_device_register_with_groups. However, it is device managed, meaning the
61	hwmon device does not have to be removed explicitly by the removal function.
62	
63	hwmon_device_unregister deregisters a registered hardware monitoring device.
64	The parameter of this function is the pointer to the registered hardware
65	monitoring device structure. This function must be called from the driver
66	remove function if the hardware monitoring device was registered with
67	hwmon_device_register or with hwmon_device_register_with_groups.
68	
69	devm_hwmon_device_unregister does not normally have to be called. It is only
70	needed for error handling, and only needed if the driver probe fails after
71	the call to devm_hwmon_device_register_with_groups.
72	
73	The header file linux/hwmon-sysfs.h provides a number of useful macros to
74	declare and use hardware monitoring sysfs attributes.
75	
76	In many cases, you can use the exsting define DEVICE_ATTR to declare such
77	attributes. This is feasible if an attribute has no additional context. However,
78	in many cases there will be additional information such as a sensor index which
79	will need to be passed to the sysfs attribute handling function.
80	
81	SENSOR_DEVICE_ATTR and SENSOR_DEVICE_ATTR_2 can be used to define attributes
82	which need such additional context information. SENSOR_DEVICE_ATTR requires
83	one additional argument, SENSOR_DEVICE_ATTR_2 requires two.
84	
85	SENSOR_DEVICE_ATTR defines a struct sensor_device_attribute variable.
86	This structure has the following fields.
87	
88	struct sensor_device_attribute {
89		struct device_attribute dev_attr;
90		int index;
91	};
92	
93	You can use to_sensor_dev_attr to get the pointer to this structure from the
94	attribute read or write function. Its parameter is the device to which the
95	attribute is attached.
96	
97	SENSOR_DEVICE_ATTR_2 defines a struct sensor_device_attribute_2 variable,
98	which is defined as follows.
99	
100	struct sensor_device_attribute_2 {
101		struct device_attribute dev_attr;
102		u8 index;
103		u8 nr;
104	};
105	
106	Use to_sensor_dev_attr_2 to get the pointer to this structure. Its parameter
107	is the device to which the attribute is attached.
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