diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index a0362d5a911e..a571495a9ac6 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1504,6 +1504,10 @@ and is between 256 and 4096 characters. It is defined in the file
 
 	rootfstype=	[KNL] Set root filesystem type
 
+	rootwait	[KNL] Wait (indefinitely) for root device to show up.
+			Useful for devices that are detected asynchronously
+			(e.g. USB and MMC devices).
+
 	rw		[KNL] Mount root device read-write on boot
 
 	S		[KNL] Run init in single mode
diff --git a/init/do_mounts.c b/init/do_mounts.c
index 46fe407fb03e..4efa1e5385e3 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -25,6 +25,7 @@ int __initdata rd_doload;	/* 1 = load RAM disk, 0 = don't load */
 int root_mountflags = MS_RDONLY | MS_SILENT;
 char * __initdata root_device_name;
 static char __initdata saved_root_name[64];
+static int __initdata root_wait;
 
 dev_t ROOT_DEV;
 
@@ -216,6 +217,16 @@ static int __init root_dev_setup(char *line)
 
 __setup("root=", root_dev_setup);
 
+static int __init rootwait_setup(char *str)
+{
+	if (*str)
+		return 0;
+	root_wait = 1;
+	return 1;
+}
+
+__setup("rootwait", rootwait_setup);
+
 static char * __initdata root_mount_data;
 static int __init root_data_setup(char *str)
 {
@@ -438,11 +449,20 @@ void __init prepare_namespace(void)
 			root_device_name += 5;
 	}
 
-	is_floppy = MAJOR(ROOT_DEV) == FLOPPY_MAJOR;
-
 	if (initrd_load())
 		goto out;
 
+	/* wait for any asynchronous scanning to complete */
+	if ((ROOT_DEV == 0) && root_wait) {
+		printk(KERN_INFO "Waiting for root device %s...\n",
+			saved_root_name);
+		while (driver_probe_done() != 0 ||
+			(ROOT_DEV = name_to_dev_t(saved_root_name)) == 0)
+			msleep(100);
+	}
+
+	is_floppy = MAJOR(ROOT_DEV) == FLOPPY_MAJOR;
+
 	if (is_floppy && rd_doload && rd_load_disk(0))
 		ROOT_DEV = Root_RAM0;