libata: assume ATA_DEV_ATA on diagnostic failure

Certain device which reports diagnostic failure also reports invalid
device signature.  Assume ATA_DEV_ATA on diagnostic failure if reset
indicates device presence.

This is fix for bugzilla bug 8784.

  http://bugzilla.kernel.org/show_bug.cgi?id=8784

Signed-off-by: Tejun Heo <htejun@gmail.com>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Edward Amsden <amsden_linux@earthlink.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/libata-core.c

@@ -751,10 +751,20 @@ unsigned int ata_dev_try_classify(struct ata_device *dev, int present,
 	/* determine if device is ATA or ATAPI */
 	class = ata_dev_classify(&tf);
 
-	if (class == ATA_DEV_UNKNOWN)
-		return ATA_DEV_NONE;
-	if ((class == ATA_DEV_ATA) && (ata_chk_status(ap) == 0))
-		return ATA_DEV_NONE;
+	if (class == ATA_DEV_UNKNOWN) {
+		/* If the device failed diagnostic, it's likely to
+		 * have reported incorrect device signature too.
+		 * Assume ATA device if the device seems present but
+		 * device signature is invalid with diagnostic
+		 * failure.
+		 */
+		if (present && (dev->horkage & ATA_HORKAGE_DIAGNOSTIC))
+			class = ATA_DEV_ATA;
+		else
+			class = ATA_DEV_NONE;
+	} else if ((class == ATA_DEV_ATA) && (ata_chk_status(ap) == 0))
+		class = ATA_DEV_NONE;
+
 	return class;
 }