linux/Documentation/driver-model/device.txt
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   1
   2The Basic Device Structure
   3~~~~~~~~~~~~~~~~~~~~~~~~~~
   4
   5struct 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
  35Fields 
  36~~~~~~
  37g_list: Node in the global device list.
  38
  39node:   Node in device's parent's children list.
  40
  41bus_list: Node in device's bus's devices list.
  42
  43driver_list:   Node in device's driver's devices list.
  44
  45intf_list:     List of intf_data. There is one structure allocated for
  46               each interface that the device supports.
  47
  48children:      List of child devices.
  49
  50parent:        *** FIXME ***
  51
  52name:          ASCII description of device. 
  53               Example: " 3Com Corporation 3c905 100BaseTX [Boomerang]"
  54
  55bus_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
  63lock:          Spinlock for the device. 
  64
  65refcount:      Reference count on the device.
  66
  67bus:           Pointer to struct bus_type that device belongs to.
  68
  69dir:           Device's sysfs directory.
  70
  71class_num:     Class-enumerated value of the device.
  72
  73driver:        Pointer to struct device_driver that controls the device.
  74
  75driver_data:   Driver-specific data.
  76
  77platform_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
  87current_state: Current power state of the device.
  88
  89saved_state:   Pointer to saved state of the device. This is usable by
  90               the device driver controlling the device.
  91
  92release:       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
  97Programming Interface
  98~~~~~~~~~~~~~~~~~~~~~
  99The bus driver that discovers the device uses this to register the
 100device with the core:
 101
 102int device_register(struct device * dev);
 103
 104The bus should initialize the following fields:
 105
 106    - parent
 107    - name
 108    - bus_id
 109    - bus
 110
 111A device is removed from the core when its reference count goes to
 1120. The reference count can be adjusted using:
 113
 114struct device * get_device(struct device * dev);
 115void put_device(struct device * dev);
 116
 117get_device() will return a pointer to the struct device passed to it
 118if the reference is not already 0 (if it's in the process of being
 119removed already).
 120
 121A driver can access the lock in the device structure using: 
 122
 123void lock_device(struct device * dev);
 124void unlock_device(struct device * dev);
 125
 126
 127Attributes
 128~~~~~~~~~~
 129struct device_attribute {
 130        struct attribute        attr;
 131        ssize_t (*show)(struct device *dev, struct device_attribute *attr,
 132                        char *buf);
 133        ssize_t (*store)(struct device *dev, struct device_attribute *attr,
 134                         const char *buf, size_t count);
 135};
 136
 137Attributes of devices can be exported via drivers using a simple
 138procfs-like interface. 
 139
 140Please see Documentation/filesystems/sysfs.txt for more information
 141on how sysfs works.
 142
 143Attributes are declared using a macro called DEVICE_ATTR:
 144
 145#define DEVICE_ATTR(name,mode,show,store)
 146
 147Example:
 148
 149DEVICE_ATTR(power,0644,show_power,store_power);
 150
 151This declares a structure of type struct device_attribute named
 152'dev_attr_power'. This can then be added and removed to the device's
 153directory using:
 154
 155int device_create_file(struct device *device, struct device_attribute * entry);
 156void device_remove_file(struct device * dev, struct device_attribute * attr);
 157
 158Example:
 159
 160device_create_file(dev,&dev_attr_power);
 161device_remove_file(dev,&dev_attr_power);
 162
 163The file name will be 'power' with a mode of 0644 (-rw-r--r--).
 164
 165