libata: allow LLDs w/o any reset method

Some old SFF controllers don't have any way to reset the channel.
Currently, this isn't supported and libata EH causes an oops.  Allow
LLDs w/o any reset method and just assume ATA class in such cases.
Signed-off-by: NTejun Heo <htejun@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/ata/libata-eh.c

@@ -2150,6 +2150,15 @@ int ata_eh_reset(struct ata_link *link, int classify,
 			ap->ops->set_piomode(ap, dev);
 	}
 
+	if (!softreset && !hardreset) {
+		if (verbose)
+			ata_link_printk(link, KERN_INFO, "no reset method "
+					"available, skipping reset\n");
+		if (!(lflags & ATA_LFLAG_ASSUME_CLASS))
+			lflags |= ATA_LFLAG_ASSUME_ATA;
+		goto done;
+	}
+
 	/* Determine which reset to use and record in ehc->i.action.
 	 * prereset() may examine and modify it.
 	 */
@@ -2254,6 +2263,7 @@ int ata_eh_reset(struct ata_link *link, int classify,
 		lflags |= ATA_LFLAG_ASSUME_ATA;
 	}
 
+ done:
 	ata_link_for_each_dev(dev, link) {
 		/* After the reset, the device state is PIO 0 and the
 		 * controller state is undefined.  Reset also wakes up