sata_mv: don't read hc_irq_cause

Remove silly read-modify-write sequences when clearing interrupts
in hc_irq_cause.  This gets rid of unneeded MMIO reads, resulting in
a slight performance boost when switching between EDMA and non-EDMA
modes (eg. for cache flushes).

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 5 insertions, 12 deletions

diff --git a/drivers/ata/sata_mv.c b/drivers/ata/sata_mv.c
index ce9d6ad5a64f..68096289074b 100644
--- a/drivers/ata/sata_mv.c
+++ b/drivers/ata/sata_mv.c
@@ -35,8 +35,6 @@
  *
  * --> Investigate problems with PCI Message Signalled Interrupts (MSI).
  *
- * --> Cache frequently-accessed registers in mv_port_priv to reduce overhead.
- *
  * --> Develop a low-power-consumption strategy, and implement it.
  *
  * --> [Experiment, low priority] Investigate interrupt coalescing.
@@ -884,18 +882,14 @@ static void mv_start_dma(struct ata_port *ap, void __iomem *port_mmio,
                 int hardport = mv_hardport_from_port(ap->port_no);
                 void __iomem *hc_mmio = mv_hc_base_from_port(
                                         mv_host_base(ap->host), ap->port_no);
-                u32 hc_irq_cause, ipending;
+                u32 hc_irq_cause;
 
                 /* clear EDMA event indicators, if any */
                 writelfl(0, port_mmio + EDMA_ERR_IRQ_CAUSE_OFS);
 
-                /* clear EDMA interrupt indicator, if any */
-                hc_irq_cause = readl(hc_mmio + HC_IRQ_CAUSE_OFS);
-                ipending = (DEV_IRQ | DMA_IRQ) << hardport;
-                if (hc_irq_cause & ipending) {
-                        writelfl(hc_irq_cause & ~ipending,
-                                 hc_mmio + HC_IRQ_CAUSE_OFS);
-                }
+                /* clear pending irq events */
+                hc_irq_cause = ~((DEV_IRQ | DMA_IRQ) << hardport);
+                writelfl(hc_irq_cause, hc_mmio + HC_IRQ_CAUSE_OFS);
 
                 mv_edma_cfg(ap, want_ncq);
 
@@ -2821,8 +2815,7 @@ static void mv_eh_thaw(struct ata_port *ap)
         writel(0, port_mmio + EDMA_ERR_IRQ_CAUSE_OFS);
 
         /* clear pending irq events */
-        hc_irq_cause = readl(hc_mmio + HC_IRQ_CAUSE_OFS);
-        hc_irq_cause &= ~((DEV_IRQ | DMA_IRQ) << hardport);
+        hc_irq_cause = ~((DEV_IRQ | DMA_IRQ) << hardport);
         writelfl(hc_irq_cause, hc_mmio + HC_IRQ_CAUSE_OFS);
 
         mv_enable_port_irqs(ap, ERR_IRQ);