[SCSI] hpsa: do not read from controller unnecessarily in completion code

MSI/MSI-X interrupts can't race the DMA completion they are communicating
so no need to read from controller to flush the DMA to the host if
MSI or MSI-X interrupts are being used.
Signed-off-by: NStephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: NJames Bottomley <JBottomley@Parallels.com>

drivers/scsi/hpsa.h

@@ -258,12 +258,12 @@ static unsigned long SA5_performant_completed(struct ctlr_info *h)
 {
 	unsigned long register_value = FIFO_EMPTY;
 
-	/* flush the controller write of the reply queue by reading
-	 * outbound doorbell status register.
-	 */
-	register_value = readl(h->vaddr + SA5_OUTDB_STATUS);
 	/* msi auto clears the interrupt pending bit. */
 	if (!(h->msi_vector || h->msix_vector)) {
+		/* flush the controller write of the reply queue by reading
+		 * outbound doorbell status register.
+		 */
+		register_value = readl(h->vaddr + SA5_OUTDB_STATUS);
 		writel(SA5_OUTDB_CLEAR_PERF_BIT, h->vaddr + SA5_OUTDB_CLEAR);
 		/* Do a read in order to flush the write to the controller
 		 * (as per spec.)