For each node in the kernel device tree, the system selects a driver for the node based on the node name and the compatible property (see Binding a Driver to a Device). The same driver might bind to multiple device nodes. The driver can differentiate different nodes by instance numbers assigned by the system.
After a driver is selected for a device node, the driver's probe(9E) entry point is called to determine the presence of the device on the system. If probe() is successful, the driver's attach(9E) entry point is invoked to set up and manage the device. The device can be opened if and only if attach() returns success (see attach() Entry Point).
A device might be unconfigured to conserve system memory resources or to enable the device to be removed while the system is still running. To enable the device to be unconfigured, the system first checks whether the device instance is referenced. This check involves calling the driver's getinfo(9E) entry point to obtain information known only to the driver (see getinfo() Entry Point). If the device instance is not referenced, the driver's detach(9E) routine is invoked to unconfigure the device (see detach() Entry Point).
To recap, each driver must define the following entry points that are used by the kernel for device configuration:
Note that attach(), detach(), and getinfo() are required. probe() is only required for devices that cannot identify themselves. For self-identifying devices, an explicit probe() routine can be provided, or nulldev(9F) can be specified in the dev_ops structure for the probe() entry point.