diff --git a/src/calibre/devices/winusb.py b/src/calibre/devices/winusb.py
index ed81863bcd..b343d61ec7 100644
--- a/src/calibre/devices/winusb.py
+++ b/src/calibre/devices/winusb.py
@@ -511,6 +511,33 @@ def get_device_interface_detail_data(dev_list, p_interface_data, buf=None):
 
 # }}}
 
+# Enumerate USB devices {{{
+
+USBDevice = namedtuple('USBDevice', 'vendor_id product_id bcd devid devinst')
+
+def iterusbdevices():
+    buf = None
+    pat = devid_pat()
+    for dev_list, devinfo in DeviceSet(guid=None, enumerator='USB', flags=DIGCF_PRESENT | DIGCF_ALLCLASSES).devices():
+        buf, devid = get_device_registry_property(dev_list, byref(devinfo), buf=buf)
+        if devid:
+            devid = devid[0].lower()
+            m = pat.search(devid)
+            if m is None:
+                yield USBDevice(None, None, None, devid, devinfo.DevInst)
+            else:
+                try:
+                    vid, pid, bcd = map(lambda x:int(x, 16), m.group(1, 2, 3))
+                except Exception:
+                    yield USBDevice(None, None, None, devid, devinfo.DevInst)
+                else:
+                    yield USBDevice(vid, pid, bcd, devid, devinfo.DevInst)
+
+def scan_usb_devices():
+    return tuple(iterusbdevices())
+
+# }}}
+
 def get_removable_drives(debug=False):  # {{{
     drive_map = get_all_removable_drives(allow_fixed=False)
     if debug:
@@ -540,41 +567,36 @@ def get_removable_drives(debug=False):  # {{{
     return ans
 # }}}
 
-def get_drive_letters_for_device(vendor_id, product_id, bcd=None, storage_number_map=None, debug=False):  # {{{
+def get_drive_letters_for_device(vendor_id, product_id, bcd=None, storage_number_map=None, devinst=None, debug=False):  # {{{
     '''
     Get the drive letters for a connected device with the specified USB ids. bcd
     can be either None, in which case it is not tested, or it must be a list or
     set like object containing bcds. The drive letters are sorted by storage number,
     which (I think) corresponds to the order they are exported by the firmware.
     '''
-    rbuf = None
     ans = {'pnp_id_map': {}, 'drive_letters':[]}
     sort_map = {}
 
-    # First search for a device matching the specified USB ids
-    for dev_list, devinfo in DeviceSet(enumerator='USB', flags=DIGCF_PRESENT | DIGCF_ALLCLASSES).devices():
-        rbuf, devid = get_device_registry_property(dev_list, byref(devinfo), buf=rbuf)
-        if devid:
-            m = devid_pat().search(devid[0])
-            if m is None:
-                continue
-            try:
-                vid, pid, rev = map(lambda x:int(x, 16), m.group(1, 2, 3))
-            except Exception:
-                continue
-            if vid == vendor_id and pid == product_id and (bcd is None or (bcd and rev in bcd)):
+    sn_map = get_storage_number_map(debug=debug) if storage_number_map is None else storage_number_map
+    if debug:
+        prints('Storage number map:')
+        prints(pformat(sn_map))
+    if not sn_map:
+        return ans
+
+    if devinst is None:
+        # First search for a device matching the specified USB ids
+        for usbdev in iterusbdevices():
+            if vendor_id == usbdev.vendor_id and product_id == usbdev.product_id and (
+                    bcd is None or (bcd and usbdev.bcd in bcd)):
+                devinst = usbdev.devinst
                 break
     else:
         if debug:
             prints('Could not find device matching vid=0x%x pid=0x%x' % (vendor_id, product_id))
         return ans
 
-    # Get the device ids for all descendants of the found device
-    sn_map = get_storage_number_map(debug=debug) if storage_number_map is None else storage_number_map
-    if debug:
-        prints('Storage number map:')
-        prints(pformat(sn_map))
-    descendants = frozenset(iterdescendants(devinfo.DevInst))
+    descendants = frozenset(iterdescendants(devinst))
     for devinfo, devpath in DeviceSet(GUID_DEVINTERFACE_DISK).interfaces():
         if devinfo.DevInst in descendants:
             if debug:
@@ -624,12 +646,7 @@ def get_storage_number_map(drive_types=(DRIVE_REMOVABLE, DRIVE_FIXED), debug=Fal
 # }}}
 
 def get_usb_devices():  # {{{
-    ans, buf = [], None
-    for dev_list, devinfo in DeviceSet(guid=None, enumerator='USB', flags=DIGCF_PRESENT | DIGCF_ALLCLASSES).devices():
-        buf, devid = get_device_registry_property(dev_list, byref(devinfo), buf=buf)
-        if devid:
-            ans.append(devid[0].lower())
-    return ans
+    return list(x.devid for x in iterusbdevices())
 # }}}
 
 def is_usb_device_connected(vendor_id, product_id):  # {{{