2 files changed, 26 insertions, 2 deletions

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;