Documentation/driver-model/device.txt

   1
   2 The Basic Device Structure
   3 ~~~~~~~~~~~~~~~~~~~~~~~~~~
   4
   5 struct device {
   6         struct list_head g_list;
   7         struct list_head node;
   8         struct list_head bus_list;
   9         struct list_head driver_list;
  10         struct list_head intf_list;
  11         struct list_head children;
  12         struct device   * parent;
  13
  14         char    name[DEVICE_NAME_SIZE];
  15         char    bus_id[BUS_ID_SIZE];
  16
  17         spinlock_t      lock;
  18         atomic_t        refcount;
  19
  20         struct bus_type * bus;
  21         struct driver_dir_entry dir;
  22
  23         u32             class_num;
  24
  25         struct device_driver *driver;
  26         void            *driver_data;
  27         void            *platform_data;
  28
  29         u32             current_state;
  30         unsigned char *saved_state;
  31
  32         void    (*release)(struct device * dev);
  33 };
  34
  35 Fields
  36 ~~~~~~
  37 g_list: Node in the global device list.
  38
  39 node:   Node in device's parent's children list.
  40
  41 bus_list: Node in device's bus's devices list.
  42
  43 driver_list:   Node in device's driver's devices list.
  44
  45 intf_list:     List of intf_data. There is one structure allocated for
  46                each interface that the device supports.
  47
  48 children:      List of child devices.
  49
  50 parent:        *** FIXME ***
  51
  52 name:          ASCII description of device.
  53                Example: " 3Com Corporation 3c905 100BaseTX [Boomerang]"
  54
  55 bus_id:        ASCII representation of device's bus position. This
  56                field should be a name unique across all devices on the
  57                bus type the device belongs to.
  58
  59                Example: PCI bus_ids are in the form of
  60                <bus number>:<slot number>.<function number>
  61                This name is unique across all PCI devices in the system.
  62
  63 lock:          Spinlock for the device.
  64
  65 refcount:      Reference count on the device.
  66
  67 bus:           Pointer to struct bus_type that device belongs to.
  68
  69 dir:           Device's sysfs directory.
  70
  71 class_num:     Class-enumerated value of the device.
  72
  73 driver:        Pointer to struct device_driver that controls the device.
  74
  75 driver_data:   Driver-specific data.
  76
  77 platform_data: Platform data specific to the device.
  78
  79                Example:  for devices on custom boards, as typical of embedded
  80                and SOC based hardware, Linux often uses platform_data to point
  81                to board-specific structures describing devices and how they
  82                are wired.  That can include what ports are available, chip
  83                variants, which GPIO pins act in what additional roles, and so
  84                on.  This shrinks the "Board Support Packages" (BSPs) and
  85                minimizes board-specific #ifdefs in drivers.
  86
  87 current_state: Current power state of the device.
  88
  89 saved_state:   Pointer to saved state of the device. This is usable by
  90                the device driver controlling the device.
  91
  92 release:       Callback to free the device after all references have
  93                gone away. This should be set by the allocator of the
  94                device (i.e. the bus driver that discovered the device).
  95
  96
  97 Programming Interface
  98 ~~~~~~~~~~~~~~~~~~~~~
  99 The bus driver that discovers the device uses this to register the
 100 device with the core:
 101
 102 int device_register(struct device * dev);
 103
 104 The bus should initialize the following fields:
 105
 106     - parent
 107     - name
 108     - bus_id
 109     - bus
 110
 111 A device is removed from the core when its reference count goes to
 112 0. The reference count can be adjusted using:
 113
 114 struct device * get_device(struct device * dev);
 115 void put_device(struct device * dev);
 116
 117 get_device() will return a pointer to the struct device passed to it
 118 if the reference is not already 0 (if it's in the process of being
 119 removed already).
 120
 121 A driver can access the lock in the device structure using:
 122
 123 void lock_device(struct device * dev);
 124 void unlock_device(struct device * dev);
 125
 126
 127 Attributes
 128 ~~~~~~~~~~
 129 struct device_attribute {
 130         struct attribute        attr;
 131         ssize_t (*show)(struct device * dev, char * buf, size_t count, loff_t off);
 132         ssize_t (*store)(struct device * dev, const char * buf, size_t count, loff_t off);
 133 };
 134
 135 Attributes of devices can be exported via drivers using a simple
 136 procfs-like interface.
 137
 138 Please see Documentation/filesystems/sysfs.txt for more information
 139 on how sysfs works.
 140
 141 Attributes are declared using a macro called DEVICE_ATTR:
 142
 143 #define DEVICE_ATTR(name,mode,show,store)
 144
 145 Example:
 146
 147 DEVICE_ATTR(power,0644,show_power,store_power);
 148
 149 This declares a structure of type struct device_attribute named
 150 'dev_attr_power'. This can then be added and removed to the device's
 151 directory using:
 152
 153 int device_create_file(struct device *device, struct device_attribute * entry);
 154 void device_remove_file(struct device * dev, struct device_attribute * attr);
 155
 156 Example:
 157
 158 device_create_file(dev,&dev_attr_power);
 159 device_remove_file(dev,&dev_attr_power);
 160
 161 The file name will be 'power' with a mode of 0644 (-rw-r--r--).
 162