[PATCH 2.6.20] sata_nv: don't rely on NV_INT_DEV indication with ADMA

[Robert Hancock <hancockr@shaw.ca>]

OK, here it is in full signed-off glory. Hopefully we can get this in 
for 2.6.20.

---

Several people reported issues with certain drive commands timing out on 
sata_nv controllers running in ADMA mode. The commands in question were 
non-DMA-mapped commands, usually FLUSH CACHE or FLUSH CACHE EXT.

From experimentation it appears that the NV_INT_DEV indication isn't 
always set when a legitimate command completion interrupt is received on 
a legacy-mode command, at least not on these controllers in ADMA mode. 
When a command is pending on the port, force the flag on always in the 
irq_stat value before calling nv_host_intr so that the drive busy state 
is always checked by ata_host_intr.

This also fixes some questionable code in nv_host_intr which called 
ata_check_status when a command was pending and ata_host_intr returned 
"unhandled". If the device interrupted at just the wrong time this could 
cause interrupts to be lost.

Signed-off-by: Robert Hancock <hancockr@shaw.ca>

--- linux-2.6.20-rc5/drivers/ata/sata_nv.c	2007-01-19 19:18:53.000000000 -0600
+++ linux-2.6.20-rc5debug/drivers/ata/sata_nv.c	2007-01-22 22:33:43.000000000 -0600
@@ -700,7 +700,6 @@ static void nv_adma_check_cpb(struct ata
 static int nv_host_intr(struct ata_port *ap, u8 irq_stat)
 {
 	struct ata_queued_cmd *qc = ata_qc_from_tag(ap, ap->active_tag);
-	int handled;
 
 	/* freeze if hotplugged */
 	if (unlikely(irq_stat & (NV_INT_ADDED | NV_INT_REMOVED))) {
@@ -719,13 +718,7 @@ static int nv_host_intr(struct ata_port 
 	}
 
 	/* handle interrupt */
-	handled = ata_host_intr(ap, qc);
-	if (unlikely(!handled)) {
-		/* spurious, clear it */
-		ata_check_status(ap);
-	}
-
-	return 1;
+	return ata_host_intr(ap, qc);
 }
 
 static irqreturn_t nv_adma_interrupt(int irq, void *dev_instance)
@@ -752,6 +745,11 @@ static irqreturn_t nv_adma_interrupt(int
 			if (pp->flags & NV_ADMA_PORT_REGISTER_MODE) {
 				u8 irq_stat = readb(host->mmio_base + NV_INT_STATUS_CK804)
 					>> (NV_INT_PORT_SHIFT * i);
+				if(ata_tag_valid(ap->active_tag))
+					/** NV_INT_DEV indication seems unreliable at times
+					    at least in ADMA mode. Force it on always when a
+					    command is active, to prevent losing interrupts. */
+					irq_stat |= NV_INT_DEV;
 				handled += nv_host_intr(ap, irq_stat);
 				continue;
 			}