libata: limit post SRST nsect/lbal wait to ~100ms

After SRST, libata used to wait for nsect/lbal to be set to 1/1 for
the slave device.  However, some ATAPI devices don't set nsect/lbal
after SRST and the wait itself isn't too useful as we're gonna wait
for !BSY right after that anyway.

Before reset-seq update, nsect/lbal wait failure used to be ignored
and caused 30sec delay during detection.  After reset-seq, all
timeouts are considered error conditions making libata fail to detect
such ATAPI devices.

This patch limits nsect/lbal wait to around 100ms.  This should give
acceptable behavior to such ATAPI devices while not disturbing the
heavily used code path too much.
Signed-off-by: NTejun Heo <htejun@gmail.com>
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/ata/libata-core.c

@@ -3061,22 +3061,28 @@ static int ata_bus_post_reset(struct ata_port *ap, unsigned int devmask,
 		}
 	}
 
-	/* if device 1 was found in ata_devchk, wait for
-	 * register access, then wait for BSY to clear
+	/* if device 1 was found in ata_devchk, wait for register
+	 * access briefly, then wait for BSY to clear.
 	 */
-	while (dev1) {
-		u8 nsect, lbal;
+	if (dev1) {
+		int i;
 
 		ap->ops->dev_select(ap, 1);
-		nsect = ioread8(ioaddr->nsect_addr);
-		lbal = ioread8(ioaddr->lbal_addr);
-		if ((nsect == 1) && (lbal == 1))
-			break;
-		if (time_after(jiffies, deadline))
-			return -EBUSY;
-		msleep(50);	/* give drive a breather */
-	}
-	if (dev1) {
+
+		/* Wait for register access.  Some ATAPI devices fail
+		 * to set nsect/lbal after reset, so don't waste too
+		 * much time on it.  We're gonna wait for !BSY anyway.
+		 */
+		for (i = 0; i < 2; i++) {
+			u8 nsect, lbal;
+
+			nsect = ioread8(ioaddr->nsect_addr);
+			lbal = ioread8(ioaddr->lbal_addr);
+			if ((nsect == 1) && (lbal == 1))
+				break;
+			msleep(50);	/* give drive a breather */
+		}
+
 		rc = ata_wait_ready(ap, deadline);
 		if (rc) {
 			if (rc != -ENODEV)