[PATCH] libata: implement presence detection via polling IDENTIFY

On some controllers (ICHs in piix mode), there is *NO* reliable way to
determine device presence other than issuing IDENTIFY and see how the
transaction proceeds by watching the TF status register.

libata acted this way before irq-pio and phantom devices caused very
little problem but now that IDENTIFY is performed using IRQ drive PIO,
such phantom devices now result in multiple 30sec timeouts during
boot.

This patch implements ATA_FLAG_DETECT_POLLING.  If a LLD sets this
flag, libata core issues the initial IDENTIFY in polling mode and if
the initial data transfer fails w/ HSM violation, the port is
considered to be empty thus replicating the old libata and IDE
behavior.

Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/libata-eh.c

@@ -1667,12 +1667,23 @@ static int ata_eh_revalidate_and_attach(struct ata_port *ap,
 			   ata_class_enabled(ehc->classes[dev->devno])) {
 			dev->class = ehc->classes[dev->devno];
 
+			if (ap->flags & ATA_FLAG_DETECT_POLLING)
+				readid_flags |= ATA_READID_DETECT;
+
 			rc = ata_dev_read_id(dev, &dev->class, readid_flags,
 					     dev->id);
 			if (rc == 0) {
 				ehc->i.flags |= ATA_EHI_PRINTINFO;
 				rc = ata_dev_configure(dev);
 				ehc->i.flags &= ~ATA_EHI_PRINTINFO;
+			} else if (rc == -ENOENT) {
+				/* IDENTIFY was issued to non-existent
+				 * device.  No need to reset.  Just
+				 * thaw and kill the device.
+				 */
+				ata_eh_thaw_port(ap);
+				dev->class = ATA_DEV_UNKNOWN;
+				rc = 0;
 			}
 
 			if (rc) {
@@ -1680,12 +1691,14 @@ static int ata_eh_revalidate_and_attach(struct ata_port *ap,
 				break;
 			}
 
-			spin_lock_irqsave(ap->lock, flags);
-			ap->pflags |= ATA_PFLAG_SCSI_HOTPLUG;
-			spin_unlock_irqrestore(ap->lock, flags);
+			if (ata_dev_enabled(dev)) {
+				spin_lock_irqsave(ap->lock, flags);
+				ap->pflags |= ATA_PFLAG_SCSI_HOTPLUG;
+				spin_unlock_irqrestore(ap->lock, flags);
 
-			/* new device discovered, configure transfer mode */
-			ehc->i.flags |= ATA_EHI_SETMODE;
+				/* new device discovered, configure xfermode */
+				ehc->i.flags |= ATA_EHI_SETMODE;
+			}
 		}
 	}