Monday, March 3, 2014

What is a Linux Device Driver Model ?

The Linux Device model is built around the concept of busses, devices and drivers. All devices in the system are connected to a bus of some kind. The bus does not have to be a real one; busses primarily exist to gather similar devices together and coordinate initialization, shutdown and power management.

When a device in the system is found to match a driver, they are bound together. The specifics about how to match devices and drivers are bus-specific. The PCI bus, for example, compares the PCI Device ID of each device against a table of supported PCI IDs provided by the driver. The platform bus, on the other hand, simply compares the name of each device against the name of each driver; if they are the same, the device matches the driver.

Binding a device to a driver involves calling the driver’s probe() function passing a pointer to the device as a parameter. From this point on, it’s the responsibility of the driver to get the device properly initialized and register it with any appropriate subsystems.

Devices that can be hot-plugged must be un-bound from the driver when they are
removed from the system. This involves calling the driver’s remove() function passing a pointer to the device as a parameter. This also happens if the driver is a dynamically loadable module and the module is unloaded. All device driver callbacks, including probe() and remove(), must follow the return
value.

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