libnvdimm: Debug probe times

Instrument nvdimm_bus_probe() to emit timestamps for the start and end
of libnvdimm device probing. This is useful for identifying sources of
libnvdimm sub-system initialization latency.
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/bus.c

@@ -100,6 +100,9 @@ static int nvdimm_bus_probe(struct device *dev)
 	if (!try_module_get(provider))
 		return -ENXIO;
 
+	dev_dbg(&nvdimm_bus->dev, "START: %s.probe(%s)\n",
+			dev->driver->name, dev_name(dev));
+
 	nvdimm_bus_probe_start(nvdimm_bus);
 	rc = nd_drv->probe(dev);
 	if (rc == 0)
@@ -108,7 +111,7 @@ static int nvdimm_bus_probe(struct device *dev)
 		nd_region_disable(nvdimm_bus, dev);
 	nvdimm_bus_probe_end(nvdimm_bus);
 
-	dev_dbg(&nvdimm_bus->dev, "%s.probe(%s) = %d\n", dev->driver->name,
+	dev_dbg(&nvdimm_bus->dev, "END: %s.probe(%s) = %d\n", dev->driver->name,
 			dev_name(dev), rc);
 
 	if (rc != 0)