Consolidate driver_probe_done() loops into one place

there's a few places that currently loop over driver_probe_done(), and
I'm about to add another one. This patch abstracts it into a helper
to reduce duplication.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Len Brown <lenb@kernel.org>
Acked-by: Greg KH <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/init/do_mounts.c b/init/do_mounts.c
index 708105e..8d4ff5a 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -370,10 +370,14 @@
 		ssleep(root_delay);
 	}
 
-	/* wait for the known devices to complete their probing */
-	while (driver_probe_done() != 0)
-		msleep(100);
-	async_synchronize_full();
+	/*
+	 * wait for the known devices to complete their probing
+	 *
+	 * Note: this is a potential source of long boot delays.
+	 * For example, it is not atypical to wait 5 seconds here
+	 * for the touchpad of a laptop to initialize.
+	 */
+	wait_for_device_probe();
 
 	md_run_setup();
 
@@ -399,6 +403,7 @@
 		while (driver_probe_done() != 0 ||
 			(ROOT_DEV = name_to_dev_t(saved_root_name)) == 0)
 			msleep(100);
+		async_synchronize_full();
 	}
 
 	is_floppy = MAJOR(ROOT_DEV) == FLOPPY_MAJOR;