ide: clear bmdma status in ide_intr() for ICHx controllers (revised #4)

patch 1/2 (revised):
- Fix drive->waiting_for_dma to work with CDB-intr devices.
- Do the dma status clearing in ide_intr() and add a new
  hwif->ide_dma_clear_irq for Intel ICHx controllers.

Revised per Alan, Sergei and Bart's advice.

Patch against 2.6.20-rc6. Tested ok on my ICH4 and pdc20275 adapters.
Please review/apply, thanks.

Signed-off-by: Albert Lee <albertcc@tw.ibm.com>
Cc: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: "Adam W. Hawks" <awhawks@us.ibm.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/ide-io.c

@@ -1646,6 +1646,17 @@ irqreturn_t ide_intr (int irq, void *dev_id)
 	del_timer(&hwgroup->timer);
 	spin_unlock(&ide_lock);
 
+	/* Some controllers might set DMA INTR no matter DMA or PIO;
+	 * bmdma status might need to be cleared even for
+	 * PIO interrupts to prevent spurious/lost irq.
+	 */
+	if (hwif->ide_dma_clear_irq && !(drive->waiting_for_dma))
+		/* ide_dma_end() needs bmdma status for error checking.
+		 * So, skip clearing bmdma status here and leave it
+		 * to ide_dma_end() if this is dma interrupt.
+		 */
+		hwif->ide_dma_clear_irq(drive);
+
 	if (drive->unmask)
 		local_irq_enable_in_hardirq();
 	/* service this interrupt, may set handler for next interrupt */