libata sata_qstor workaround for spurious interrupts

sata_qstor workaround for spurious interrupts.

The qstor hardware generates spurious interrupts from time to time when
switching in and out of packet mode.  These eventually result in the
IRQ being disabled, which kills other devices sharing this IRQ with us.

This workaround isn't perfect, but it's about the best we can do for
this hardware.  Spurious interrupts will still happen, but won't be
logged as such, and therefore won't cause the IRQ to be inadvertently
disabled.

Signed-off-by:  Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/sata_qstor.c

@@ -425,24 +425,27 @@ static inline unsigned int qs_intr_mmio(struct ata_host *host)
 		if (ap &&
 		    !(ap->flags & ATA_FLAG_DISABLED)) {
 			struct ata_queued_cmd *qc;
-			struct qs_port_priv *pp = ap->private_data;
+			struct qs_port_priv *pp;
+			qc = ata_qc_from_tag(ap, ap->link.active_tag);
+			if (!qc || !(qc->flags & ATA_QCFLAG_ACTIVE)) {
+				/*
+				 * The qstor hardware generates spurious
+				 * interrupts from time to time when switching
+				 * in and out of packet mode.
+				 * There's no obvious way to know if we're
+				 * here now due to that, so just ack the irq
+				 * and pretend we knew it was ours.. (ugh).
+				 * This does not affect packet mode.
+				 */
+				ata_check_status(ap);
+				handled = 1;
+				continue;
+			}
+			pp = ap->private_data;
 			if (!pp || pp->state != qs_state_mmio)
 				continue;
-			qc = ata_qc_from_tag(ap, ap->link.active_tag);
-			if (qc && (!(qc->tf.flags & ATA_TFLAG_POLLING))) {
-
-				/* check main status, clearing INTRQ */
-				u8 status = ata_check_status(ap);
-				if ((status & ATA_BUSY))
-					continue;
-				DPRINTK("ata%u: protocol %d (dev_stat 0x%X)\n",
-					ap->print_id, qc->tf.protocol, status);
-
-				/* complete taskfile transaction */
-				qc->err_mask |= ac_err_mask(status);
-				ata_qc_complete(qc);
-				handled = 1;
-			}
+			if (!(qc->tf.flags & ATA_TFLAG_POLLING))
+				handled |= ata_host_intr(ap, qc);
 		}
 	}
 	return handled;
@@ -452,12 +455,13 @@ static irqreturn_t qs_intr(int irq, void *dev_instance)
 {
 	struct ata_host *host = dev_instance;
 	unsigned int handled = 0;
+	unsigned long flags;
 
 	VPRINTK("ENTER\n");
 
-	spin_lock(&host->lock);
+	spin_lock_irqsave(&host->lock, flags);
 	handled  = qs_intr_pkt(host) | qs_intr_mmio(host);
-	spin_unlock(&host->lock);
+	spin_unlock_irqrestore(&host->lock, flags);
 
 	VPRINTK("EXIT\n");