Quiescing Card and Driver

General

Prior to removing a card from the system, two things must occur:

How this is accomplished is OS-specific, but the following must take place:

• The OS must stop issuing new requests to the device's driver or must instruct the driver to stop accepting new requests.

• The driver must terminate or complete all outstanding requests.

• The card must be disabled from generating interrupts or transactions.

When the OS commands the driver to quiesce itself and its device, the OS must not expect the device to remain in the system (in other words, it could be removed and not replaced with a similar card).

Pausing a Driver (Optional)

Optionally, an OS could implement a "Pause" capability to temporarily stop driver activity in the expectation that the same card or a similar card will be reinserted. If the card is not reinstalled within a reasonable amount of time, however, the driver must be quiesced and then removed from memory.

A card may be removed and an identical card installed in its place. As an example, this could be because the currently-installed card is bad or is being replaced with a later revision as an upgrade. If it is intended that the operation appear seamless from a software and operational perspective, the driver would have to quiesce, save the current device's context (i.e., the contents of all of its registers, etc.). The new card would then be installed, the context restored, and normal operation would resume. It should be noted that if the old card had failed, it may or may not be possible to have the operation appear seamless.

Quiescing a Driver That Controls Multiple Devices

If a driver controls multiple cards and it receives a command from the OS to quiesce its activity with respect to a specific card, it must only quiesce its activity with that card as well as quiescing the card itself.

Quiescing a Failed Card

If a card has failed, it may not be possible for the driver to complete requests previously issued to the card. In this case, the driver must detect the error and must terminate the requests without completion and attempt to reset the card.