driver-core: add test module for asynchronous probing

This test module tries to test asynchronous driver probing by having a
driver that sleeps for an extended period of time (5 secs) in its
probe() method. It measures the time needed to register this driver
(with device already registered) and a new device (with driver already
registered). The module will fail to load if the time spent in register
call is more than half the probing sleep time.

As a sanity check the driver will then try to synchronously register
driver and device and fail if registration takes less than half of the
probing sleep time.

Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Reviewed-by: Olof Johansson <olofj@chromium.org>
Signed-off-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/test/Kconfig

@@ -0,0 +1,9 @@
+config TEST_ASYNC_DRIVER_PROBE
+	tristate "Build kernel module to test asynchronous driver probing"
+	depends on m
+	help
+	  Enabling this option produces a kernel module that allows
+	  testing asynchronous driver probing by the device core.
+	  The module name will be test_async_driver_probe.ko
+
+	  If unsure say N.