megaraid_sas: Add an i/o barrier

BugLink: http://bugs.launchpad.net/bugs/1544679

A barrier should be added to ensure proper ordering of memory mapped
writes.
Signed-off-by: Tomas Henzl <thenzl@redhat.com>
Reviewed-by: Kashyap Desai <kashyap.desai@broadcom.com>
Acked-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
(cherry picked from linux-next commit 4327614e7154a29a5db10469e49282f61598f41a)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/scsi/megaraid/megaraid_sas_base.c

@@ -749,6 +749,7 @@ megasas_fire_cmd_skinny(struct megasas_instance *instance,
 	       &(regs)->inbound_high_queue_port);
 	writel((lower_32_bits(frame_phys_addr) | (frame_count<<1))|1,
 	       &(regs)->inbound_low_queue_port);
+	mmiowb();
 	spin_unlock_irqrestore(&instance->hba_lock, flags);
 }
 

drivers/scsi/megaraid/megaraid_sas_fusion.c

@@ -204,6 +204,7 @@ megasas_fire_cmd_fusion(struct megasas_instance *instance,
 		&instance->reg_set->inbound_low_queue_port);
 	writel(le32_to_cpu(req_desc->u.high),
 		&instance->reg_set->inbound_high_queue_port);
+	mmiowb();
 	spin_unlock_irqrestore(&instance->hba_lock, flags);
 #endif
 }