[PATCH] ahci: add PIOS interim interrupt handling

During multiblock PIO, multiple PIOS interrupts are generated before
qc compltion.  Current code prints unnecessary message for such cases.
This is exposed when new EH slows down attached device into PIO mode.

Signed-off-by: Tejun Heo <htejun@gmail.com>

drivers/scsi/ahci.c

@@ -883,7 +883,18 @@ static void ahci_host_intr(struct ata_port *ap)
 		}
 	}
 
-	/* spurious interrupt */
+	/* hmmm... a spurious interupt */
+
+	/* ignore interim PIO setup fis interrupts */
+	if (ata_tag_valid(ap->active_tag)) {
+		struct ata_queued_cmd *qc =
+			ata_qc_from_tag(ap, ap->active_tag);
+
+		if (qc && qc->tf.protocol == ATA_PROT_PIO &&
+		    (status & PORT_IRQ_PIOS_FIS))
+			return;
+	}
+
 	if (ata_ratelimit())
 		ata_port_printk(ap, KERN_INFO, "spurious interrupt "
 				"(irq_stat 0x%x active_tag %d)\n",