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- The Basic Device Structure
- ~~~~~~~~~~~~~~~~~~~~~~~~~~
- struct device {
- struct list_head g_list;
- struct list_head node;
- struct list_head bus_list;
- struct list_head driver_list;
- struct list_head intf_list;
- struct list_head children;
- struct device * parent;
- char name[DEVICE_NAME_SIZE];
- char bus_id[BUS_ID_SIZE];
- spinlock_t lock;
- atomic_t refcount;
- struct bus_type * bus;
- struct driver_dir_entry dir;
- u32 class_num;
- struct device_driver *driver;
- void *driver_data;
- void *platform_data;
- u32 current_state;
- unsigned char *saved_state;
- void (*release)(struct device * dev);
- };
- Fields
- ~~~~~~
- g_list: Node in the global device list.
- node: Node in device's parent's children list.
- bus_list: Node in device's bus's devices list.
- driver_list: Node in device's driver's devices list.
- intf_list: List of intf_data. There is one structure allocated for
- each interface that the device supports.
- children: List of child devices.
- parent: *** FIXME ***
- name: ASCII description of device.
- Example: " 3Com Corporation 3c905 100BaseTX [Boomerang]"
- bus_id: ASCII representation of device's bus position. This
- field should be a name unique across all devices on the
- bus type the device belongs to.
- Example: PCI bus_ids are in the form of
- <bus number>:<slot number>.<function number>
- This name is unique across all PCI devices in the system.
- lock: Spinlock for the device.
- refcount: Reference count on the device.
- bus: Pointer to struct bus_type that device belongs to.
- dir: Device's sysfs directory.
- class_num: Class-enumerated value of the device.
- driver: Pointer to struct device_driver that controls the device.
- driver_data: Driver-specific data.
- platform_data: Platform data specific to the device.
- Example: for devices on custom boards, as typical of embedded
- and SOC based hardware, Linux often uses platform_data to point
- to board-specific structures describing devices and how they
- are wired. That can include what ports are available, chip
- variants, which GPIO pins act in what additional roles, and so
- on. This shrinks the "Board Support Packages" (BSPs) and
- minimizes board-specific #ifdefs in drivers.
- current_state: Current power state of the device.
- saved_state: Pointer to saved state of the device. This is usable by
- the device driver controlling the device.
- release: Callback to free the device after all references have
- gone away. This should be set by the allocator of the
- device (i.e. the bus driver that discovered the device).
- Programming Interface
- ~~~~~~~~~~~~~~~~~~~~~
- The bus driver that discovers the device uses this to register the
- device with the core:
- int device_register(struct device * dev);
- The bus should initialize the following fields:
- - parent
- - name
- - bus_id
- - bus
- A device is removed from the core when its reference count goes to
- 0. The reference count can be adjusted using:
- struct device * get_device(struct device * dev);
- void put_device(struct device * dev);
- get_device() will return a pointer to the struct device passed to it
- if the reference is not already 0 (if it's in the process of being
- removed already).
- A driver can access the lock in the device structure using:
- void lock_device(struct device * dev);
- void unlock_device(struct device * dev);
- Attributes
- ~~~~~~~~~~
- struct device_attribute {
- struct attribute attr;
- ssize_t (*show)(struct device * dev, char * buf, size_t count, loff_t off);
- ssize_t (*store)(struct device * dev, const char * buf, size_t count, loff_t off);
- };
- Attributes of devices can be exported via drivers using a simple
- procfs-like interface.
- Please see Documentation/filesystems/sysfs.txt for more information
- on how sysfs works.
- Attributes are declared using a macro called DEVICE_ATTR:
- #define DEVICE_ATTR(name,mode,show,store)
- Example:
- DEVICE_ATTR(power,0644,show_power,store_power);
- This declares a structure of type struct device_attribute named
- 'dev_attr_power'. This can then be added and removed to the device's
- directory using:
- int device_create_file(struct device *device, struct device_attribute * entry);
- void device_remove_file(struct device * dev, struct device_attribute * attr);
- Example:
- device_create_file(dev,&dev_attr_power);
- device_remove_file(dev,&dev_attr_power);
- The file name will be 'power' with a mode of 0644 (-rw-r--r--).
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