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-Driver Binding
-Driver binding is the process of associating a device with a device
-driver that can control it. Bus drivers have typically handled this
-because there have been bus-specific structures to represent the
-devices and the drivers. With generic device and device driver
-structures, most of the binding can take place using common code.
-The bus type structure contains a list of all devices that are on that bus
-type in the system. When device_register is called for a device, it is
-inserted into the end of this list. The bus object also contains a
-list of all drivers of that bus type. When driver_register is called
-for a driver, it is inserted at the end of this list. These are the
-two events which trigger driver binding.
-When a new device is added, the bus's list of drivers is iterated over
-to find one that supports it. In order to determine that, the device
-ID of the device must match one of the device IDs that the driver
-supports. The format and semantics for comparing IDs is bus-specific.
-Instead of trying to derive a complex state machine and matching
-algorithm, it is up to the bus driver to provide a callback to compare
-a device against the IDs of a driver. The bus returns 1 if a match was
-found; 0 otherwise.
-int match(struct device * dev, struct device_driver * drv);
-If a match is found, the device's driver field is set to the driver
-and the driver's probe callback is called. This gives the driver a
-chance to verify that it really does support the hardware, and that
-it's in a working state.
-Device Class
-Upon the successful completion of probe, the device is registered with
-the class to which it belongs. Device drivers belong to one and only one
-class, and that is set in the driver's devclass field.
-devclass_add_device is called to enumerate the device within the class
-and actually register it with the class, which happens with the
-class's register_dev callback.
-When a driver is attached to a device, the device is inserted into the
-driver's list of devices.
-A symlink is created in the bus's 'devices' directory that points to
-the device's directory in the physical hierarchy.
-A symlink is created in the driver's 'devices' directory that points
-to the device's directory in the physical hierarchy.
-A directory for the device is created in the class's directory. A
-symlink is created in that directory that points to the device's
-physical location in the sysfs tree.
-A symlink can be created (though this isn't done yet) in the device's
-physical directory to either its class directory, or the class's
-top-level directory. One can also be created to point to its driver's
-directory also.
-The process is almost identical for when a new driver is added.
-The bus's list of devices is iterated over to find a match. Devices
-that already have a driver are skipped. All the devices are iterated
-over, to bind as many devices as possible to the driver.
-When a device is removed, the reference count for it will eventually
-go to 0. When it does, the remove callback of the driver is called. It
-is removed from the driver's list of devices and the reference count
-of the driver is decremented. All symlinks between the two are removed.
-When a driver is removed, the list of devices that it supports is
-iterated over, and the driver's remove callback is called for each
-one. The device is removed from that list and the symlinks removed.