w1: add fast search for single slave bus

This enables a much more efficient way of device searching. It uses the
1-wire read-rom operation which allows the direct reading of the slave
address. BUT this works only with exactly one slave on the bus.
Signed-off-by: NHubert Feurstein <h.feurstein@gmail.com>
Acked-by: NEvgeniy Polyakov <zbr@ioremap.net>

index c374978..9761950 100644
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/w1/w1.c

@@ -892,6 +892,16 @@ void w1_search(struct w1_master *dev, u8 search_type, w1_slave_found_callback cb
 			break;
 		}
 
+		/* Do fast search on single slave bus */
+		if (dev->max_slave_count == 1) {
+			w1_write_8(dev, W1_READ_ROM);
+
+			if (w1_read_block(dev, (u8 *)&rn, 8) == 8 && rn)
+				cb(dev, rn);
+
+			break;
+		}
+
 		/* Start the search */
 		w1_write_8(dev, search_type);
 		for (i = 0; i < 64; ++i) {