[PATCH] libata: implement port_task

Implement port_task.  LLDD's can schedule a function to be executed
with context after specified delay.  libata core takes care of
synchronization against EH.  This is generalized form of pio_task and
packet_task which are tied to PIO hsm implementation.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/scsi/libata-scsi.c

@@ -785,6 +785,8 @@ int ata_scsi_error(struct Scsi_Host *host)
 	WARN_ON(ata_qc_from_tag(ap, ap->active_tag) == NULL);
 	spin_unlock_irqrestore(&ap->host_set->lock, flags);
 
+	ata_port_flush_task(ap);
+
 	ap->ops->eng_timeout(ap);
 
 	WARN_ON(host->host_failed || !list_empty(&host->eh_cmd_q));