scsi: hisi_sas: save completion queue read pointer

Optimise by saving an avoidable read in the cq interrupt.  The queue
read pointer will only be updated by software, so don't bother
re-reading what was already written in the previous interrupt.
Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hisi_sas/hisi_sas.h

@@ -94,6 +94,7 @@ struct hisi_sas_port {
 
 struct hisi_sas_cq {
 	struct hisi_hba *hisi_hba;
+	int	rd_point;
 	int	id;
 };
 

drivers/scsi/hisi_sas/hisi_sas_v1_hw.c

@@ -1565,14 +1565,11 @@ static irqreturn_t cq_interrupt_v1_hw(int irq, void *p)
 	struct hisi_sas_complete_v1_hdr *complete_queue =
 			(struct hisi_sas_complete_v1_hdr *)
 			hisi_hba->complete_hdr[queue];
-	u32 irq_value, rd_point, wr_point;
+	u32 irq_value, rd_point = cq->rd_point, wr_point;
 
 	irq_value = hisi_sas_read32(hisi_hba, OQ_INT_SRC);
 
 	hisi_sas_write32(hisi_hba, OQ_INT_SRC, 1 << queue);
-
-	rd_point = hisi_sas_read32(hisi_hba,
-			COMPL_Q_0_RD_PTR + (0x14 * queue));
 	wr_point = hisi_sas_read32(hisi_hba,
 			COMPL_Q_0_WR_PTR + (0x14 * queue));
 
@@ -1600,6 +1597,7 @@ static irqreturn_t cq_interrupt_v1_hw(int irq, void *p)
 	}
 
 	/* update rd_point */
+	cq->rd_point = rd_point;
 	hisi_sas_write32(hisi_hba, COMPL_Q_0_RD_PTR + (0x14 * queue), rd_point);
 
 	return IRQ_HANDLED;

drivers/scsi/hisi_sas/hisi_sas_v2_hw.c

@@ -2049,7 +2049,7 @@ static irqreturn_t cq_interrupt_v2_hw(int irq_no, void *p)
 	struct hisi_sas_slot *slot;
 	struct hisi_sas_itct *itct;
 	struct hisi_sas_complete_v2_hdr *complete_queue;
-	u32 irq_value, rd_point, wr_point, dev_id;
+	u32 irq_value, rd_point = cq->rd_point, wr_point, dev_id;
 	int queue = cq->id;
 
 	complete_queue = hisi_hba->complete_hdr[queue];
@@ -2057,8 +2057,6 @@ static irqreturn_t cq_interrupt_v2_hw(int irq_no, void *p)
 
 	hisi_sas_write32(hisi_hba, OQ_INT_SRC, 1 << queue);
 
-	rd_point = hisi_sas_read32(hisi_hba, COMPL_Q_0_RD_PTR +
-				   (0x14 * queue));
 	wr_point = hisi_sas_read32(hisi_hba, COMPL_Q_0_WR_PTR +
 				   (0x14 * queue));
 
@@ -2106,6 +2104,7 @@ static irqreturn_t cq_interrupt_v2_hw(int irq_no, void *p)
 	}
 
 	/* update rd_point */
+	cq->rd_point = rd_point;
 	hisi_sas_write32(hisi_hba, COMPL_Q_0_RD_PTR + (0x14 * queue), rd_point);
 	return IRQ_HANDLED;
 }