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scsi: qedi: Add support for fastpath doorvell recovery
Driver fastpath employs doorbells to indicate to the device that work is available. Each doorbell translates to a message sent to the device over the pci. These messages are queued by the doorbell queue HW block, and handled by the HW. If a sufficient amount of CPU cores are sending messages at a sufficient rate, the queue can overflow, and messages can be dropped. There are many entities in the driver which can send doorbell messages. When overflow happens, a fatal HW attention is indicated, and the Doorbell HW block stops accepting new doorbell messages until recovery procedure is done. When overflow occurs, all doorbells are dropped. Since doorbells are aggregatives, if more doorbells are sent nothing has to be done. But if the "last" doorbell is dropped, the doorbelling entity doesn’t know this happened, and may wait forever for the device to perform the action. The doorbell recovery mechanism addresses just that - it sends the last doorbell of every entity. Signed-off-by: Manish Rangankar <mrangankar@marvell.com> Signed-off-by: Shai Malin <smalin@marvell.com>
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