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-
-Device Classes
-
-
-Introduction
-~~~~~~~~~~~~
-A device class describes a type of device, like an audio or network
-device. The following device classes have been identified:
-
-<Insert List of Device Classes Here>
-
-
-Each device class defines a set of semantics and a programming interface
-that devices of that class adhere to. Device drivers are the
-implementation of that programming interface for a particular device on
-a particular bus.
-
-Device classes are agnostic with respect to what bus a device resides
-on.
-
-
-Programming Interface
-~~~~~~~~~~~~~~~~~~~~~
-The device class structure looks like:
-
-
-typedef int (*devclass_add)(struct device *);
-typedef void (*devclass_remove)(struct device *);
-
-See the kerneldoc for the struct class.
-
-A typical device class definition would look like:
-
-struct device_class input_devclass = {
- .name = "input",
- .add_device = input_add_device,
- .remove_device = input_remove_device,
-};
-
-Each device class structure should be exported in a header file so it
-can be used by drivers, extensions and interfaces.
-
-Device classes are registered and unregistered with the core using:
-
-int devclass_register(struct device_class * cls);
-void devclass_unregister(struct device_class * cls);
-
-
-Devices
-~~~~~~~
-As devices are bound to drivers, they are added to the device class
-that the driver belongs to. Before the driver model core, this would
-typically happen during the driver's probe() callback, once the device
-has been initialized. It now happens after the probe() callback
-finishes from the core.
-
-The device is enumerated in the class. Each time a device is added to
-the class, the class's devnum field is incremented and assigned to the
-device. The field is never decremented, so if the device is removed
-from the class and re-added, it will receive a different enumerated
-value.
-
-The class is allowed to create a class-specific structure for the
-device and store it in the device's class_data pointer.
-
-There is no list of devices in the device class. Each driver has a
-list of devices that it supports. The device class has a list of
-drivers of that particular class. To access all of the devices in the
-class, iterate over the device lists of each driver in the class.
-
-
-Device Drivers
-~~~~~~~~~~~~~~
-Device drivers are added to device classes when they are registered
-with the core. A driver specifies the class it belongs to by setting
-the struct device_driver::devclass field.
-
-
-sysfs directory structure
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-There is a top-level sysfs directory named 'class'.
-
-Each class gets a directory in the class directory, along with two
-default subdirectories:
-
- class/
- `-- input
- |-- devices
- `-- drivers
-
-
-Drivers registered with the class get a symlink in the drivers/ directory
-that points to the driver's directory (under its bus directory):
-
- class/
- `-- input
- |-- devices
- `-- drivers
- `-- usb:usb_mouse -> ../../../bus/drivers/usb_mouse/
-
-
-Each device gets a symlink in the devices/ directory that points to the
-device's directory in the physical hierarchy:
-
- class/
- `-- input
- |-- devices
- | `-- 1 -> ../../../root/pci0/00:1f.0/usb_bus/00:1f.2-1:0/
- `-- drivers
-
-
-Exporting Attributes
-~~~~~~~~~~~~~~~~~~~~
-struct devclass_attribute {
- struct attribute attr;
- ssize_t (*show)(struct device_class *, char * buf, size_t count, loff_t off);
- ssize_t (*store)(struct device_class *, const char * buf, size_t count, loff_t off);
-};
-
-Class drivers can export attributes using the DEVCLASS_ATTR macro that works
-similarly to the DEVICE_ATTR macro for devices. For example, a definition
-like this:
-
-static DEVCLASS_ATTR(debug,0644,show_debug,store_debug);
-
-is equivalent to declaring:
-
-static devclass_attribute devclass_attr_debug;
-
-The bus driver can add and remove the attribute from the class's
-sysfs directory using:
-
-int devclass_create_file(struct device_class *, struct devclass_attribute *);
-void devclass_remove_file(struct device_class *, struct devclass_attribute *);
-
-In the example above, the file will be named 'debug' in placed in the
-class's directory in sysfs.
-
-
-Interfaces
-~~~~~~~~~~
-There may exist multiple mechanisms for accessing the same device of a
-particular class type. Device interfaces describe these mechanisms.
-
-When a device is added to a device class, the core attempts to add it
-to every interface that is registered with the device class.
-