hpsa: avoid unnecessary readl on every command submission

for controllers which support either of the ioaccel transport methods.
Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Reviewed-by: Mike Miller <michael.miller@canonical.com>
Reviewed-by: Joe Handzik <joseph.t.handzik@hp.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/scsi/hpsa.c

@@ -7330,6 +7330,13 @@ static void hpsa_enter_performant_mode(struct ctlr_info *h, u32 trans_support)
 	 * 10 = 6 s/g entry or 24k
 	 */
 
+	/* If the controller supports either ioaccel method then
+	 * we can also use the RAID stack submit path that does not
+	 * perform the superfluous readl() after each command submission.
+	 */
+	if (trans_support & (CFGTBL_Trans_io_accel1 | CFGTBL_Trans_io_accel2))
+		access = SA5_performant_access_no_read;
+
 	/* Controller spec: zero out this buffer. */
 	for (i = 0; i < h->nreply_queues; i++)
 		memset(h->reply_queue[i].head, 0, h->reply_queue_size);

drivers/scsi/hpsa.h

@@ -346,6 +346,12 @@ static void SA5_submit_command(struct ctlr_info *h,
 	(void) readl(h->vaddr + SA5_SCRATCHPAD_OFFSET);
 }
 
+static void SA5_submit_command_no_read(struct ctlr_info *h,
+	struct CommandList *c)
+{
+	writel(c->busaddr, h->vaddr + SA5_REQUEST_PORT_OFFSET);
+}
+
 static void SA5_submit_command_ioaccel2(struct ctlr_info *h,
 	struct CommandList *c)
 {
@@ -353,7 +359,6 @@ static void SA5_submit_command_ioaccel2(struct ctlr_info *h,
 		writel(c->busaddr, h->vaddr + IOACCEL2_INBOUND_POSTQ_32);
 	else
 		writel(c->busaddr, h->vaddr + SA5_REQUEST_PORT_OFFSET);
-	(void) readl(h->vaddr + SA5_SCRATCHPAD_OFFSET);
 }
 
 /*
@@ -564,6 +569,14 @@ static struct access_method SA5_performant_access = {
 	SA5_performant_completed,
 };
 
+static struct access_method SA5_performant_access_no_read = {
+	SA5_submit_command_no_read,
+	SA5_performant_intr_mask,
+	SA5_fifo_full,
+	SA5_performant_intr_pending,
+	SA5_performant_completed,
+};
+
 struct board_type {
 	u32	board_id;
 	char	*product_name;