Hot-Plug Removal

The hot-plug removal event is typically reported via interrupts.

To be notified when the hot-plug removal occurs, the bus driver connects an interrupt handler to an appropriate interrupt source. Consider two typical mechanisms of hot-plug removal:

surprise removal

Surprise removal means a device can be removed at any time with no warning. For instance, PCMCIA is a surprise removal device.

non-surprise removal

Non-surprise removal means that the device cannot be removed until the system is prepared for it. For instance, Hot-Plug CompactPCI is a non-surprise removal device.

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.

Non-Surprise Removal

The non-surprise removal interrupt requests the bus driver to enable the device removal from the bus. This is discussed at length above (in the Surprise Removalsection). The difference between surprise and non-surprise removal is that in non-surprise removal, the bus driver requests the normal device shutdown service (DEV_SHUTDOWN) rather than the device removal service ( DEV_REMOVAL).

In addition, once the device tree is updated, the bus driver enables the device removal. Device removal enabling is usually signaled by an LED, and/or by a card ejection mechanism.