1 ==========================
2 The Basic Device Structure
3 ==========================
4
5 See the kerneldoc for the struct device.
6
7
8 Programming Interface
9 ~~~~~~~~~~~~~~~~~~~~~
10 The bus driver that discovers the device uses
11 device with the core::
12
13 int device_register(struct device * dev);
14
15 The bus should initialize the following fields
16
17 - parent
18 - name
19 - bus_id
20 - bus
21
22 A device is removed from the core when its ref
23 0. The reference count can be adjusted using::
24
25 struct device * get_device(struct device * d
26 void put_device(struct device * dev);
27
28 get_device() will return a pointer to the stru
29 if the reference is not already 0 (if it's in
30 removed already).
31
32 A driver can access the lock in the device str
33
34 void lock_device(struct device * dev);
35 void unlock_device(struct device * dev);
36
37
38 Attributes
39 ~~~~~~~~~~
40
41 ::
42
43 struct device_attribute {
44 struct attribute attr;
45 ssize_t (*show)(struct device *dev, st
46 char *buf);
47 ssize_t (*store)(struct device *dev, s
48 const char *buf, size
49 };
50
51 Attributes of devices can be exported by a dev
52
53 Please see Documentation/filesystems/sysfs.rst
54 on how sysfs works.
55
56 As explained in Documentation/core-api/kobject
57 created before the KOBJ_ADD uevent is generate
58 that is by defining an attribute group.
59
60 Attributes are declared using a macro called D
61
62 #define DEVICE_ATTR(name,mode,show,store)
63
64 Example:::
65
66 static DEVICE_ATTR(type, 0444, type_show, NU
67 static DEVICE_ATTR(power, 0644, power_show,
68
69 Helper macros are available for common values
70 can be simplified to:::
71
72 static DEVICE_ATTR_RO(type);
73 static DEVICE_ATTR_RW(power);
74
75 This declares two structures of type struct de
76 names 'dev_attr_type' and 'dev_attr_power'. Th
77 organized as follows into a group::
78
79 static struct attribute *dev_attrs[] = {
80 &dev_attr_type.attr,
81 &dev_attr_power.attr,
82 NULL,
83 };
84
85 static struct attribute_group dev_group = {
86 .attrs = dev_attrs,
87 };
88
89 static const struct attribute_group *dev_gro
90 &dev_group,
91 NULL,
92 };
93
94 A helper macro is available for the common cas
95 above two structures can be declared using:::
96
97 ATTRIBUTE_GROUPS(dev);
98
99 This array of groups can then be associated wi
100 group pointer in struct device before device_r
101
102 dev->groups = dev_groups;
103 device_register(dev);
104
105 The device_register() function will use the 'g
106 device attributes and the device_unregister()
107 to remove the device attributes.
108
109 Word of warning: While the kernel allows devi
110 device_remove_file() to be called on a device
111 strict expectations on when attributes get cre
112 registered in the kernel, a uevent is generate
113 udev) that a new device is available. If attr
114 device is registered, then userspace won't get
115 not know about the new attributes.
116
117 This is important for device driver that need
118 attributes for a device at driver probe time.
119 calls device_create_file() on the device struc
120 userspace will never be notified of the new at
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