Surprise Removal

The surprise removal interrupt notifies the bus driver that a device has been removed from the bus. The bus driver interrupt handler usually detects the removed device (and associated device node) using bus specific status register(s).

Once the device is detected, the interrupt handler checks whether the device node is active. If the device node is inactive (there is no driver instance servicing the device), the only task of the bus driver is to update the device tree removing the device node. This frees all bus resources associated with the node .

The bus driver is not able to accomplish this task immediately at interrupt level because the services used are typically not available at interrupt level. These types of services can typically be called in the DKI thread context only.

To satisfy the invocation context requirements, the bus driver calls svDkiThreadTrigger requesting the DKI thread to invoke the removal procedure. Using the DKI thread also allows you to serialize all actions related to initialization and termination operations.

If the device node is active, the bus driver must shutdown the corresponding device driver instance prior to invoking the removal procedure. To accomplish this task, the bus driver invokes the device driver event handler signaling the DEV_REMOVAL event. In fact, the bus driver performs the shutdown prolog for the given driver instance (see the "Write Event Handler Function" section). In other words, the bus driver initiates the shutdown process for the given device sub-tree. (The removed device node is the root of the sub-tree.)

As the last action in the shutdown event process, the child device driver closes the connection to the bus driver and, at this moment, the bus driver performs the removal procedure. Note that the removal procedure is executed in the DKI thread context because the close service routine is called in the DKI thread context.