Improve USB device reset logic

webrtc/tools/run_video_analysis.py

Index: webrtc/tools/run_video_analysis.py
diff --git a/webrtc/tools/run_video_analysis.py b/webrtc/tools/run_video_analysis.py
index 29682aa02917779742ececaca52b0662a6d80546..a60d035f70b0374fcb464357a48b47bf22f171f7 100755
--- a/webrtc/tools/run_video_analysis.py
+++ b/webrtc/tools/run_video_analysis.py
@@ -158,47 +158,67 @@ def CreateRecordingDirs(options):
   return record_paths
 
 
-def RestartMagewellDevices(ref_video_device, test_video_device):
-  """Reset the USB ports where Magewell capture devices are connected to.
+def FindUsbPortForV4lDevices(ref_video_device, test_video_device):

[kjellander_webrtc, 2017/03/30 15:52:42]

FindUsbPortForV4lDevices is a great candidate for a simple unit test. Can you
please write one?

[janssonWebRTC, 2017/03/31 11:55:39]

Done.

+  """Tries to find the usb port for ref_video_device and test_video_device.
 
   Tries to find the provided ref_video_device and test_video_device devices
   which use video4linux and then do a soft reset by using USB unbind and bind.
+
+  Args:
+    ref_device(string): reference recording device path.
+    test_device(string): test recording device path
+
+  Returns:
+    usb_ports(list): USB ports(string) for the devices found.
+  """
+
+  # Find the device location including USB and USB Bus ID's. Use the usb1
+  # in the path since the driver folder is a symlink which contains all the
+  # usb device port mappings and it's the same in all usbN folders.

[kjellander_webrtc, 2017/03/30 15:52:42]

Maybe mention something about (at least on Ubuntu Trusty) since I imagine other
distros may have other layouts.

[janssonWebRTC, 2017/03/31 11:55:39]

Done.

+  v4l_device_path = '/sys/bus/usb/devices/usb1/1-1/driver/**/**/video4linux/'
+  v4l_ref_device = glob.glob('%s%s' % (v4l_device_path, ref_video_device))
+  v4l_test_device = glob.glob('%s%s' % (v4l_device_path, test_video_device))
+  usb_ports = []
+  paths = []
+
+  # Split on the driver folder first since we are only interested in the
+  # folders thereafter.
+  ref_path = str(v4l_ref_device).split('driver')[1].split('/')
+  test_path = str(v4l_test_device).split('driver')[1].split('/')
+  paths.append(ref_path)
+  paths.append(test_path)
+
+  for path in paths:
+    for usb_id in path:
+      # Some motherboards have an additional USB controller/hub and hence why
+      # we need to look for two different strings.
+      # E.g "4-4.4" and "4-4".
+      if re.match(r'^\d-\d$', usb_id) or re.match(r'^\d-\d\.\d$', usb_id):
+        usb_ports.append(usb_id)
+
+  return usb_ports
+
+
+def RestartMagewellDevices(ref_video_device_path, test_video_device_path):
+  """Reset the USB ports where Magewell capture devices are connected to.
+
+  Performs a soft reset by using USB unbind and bind.
   This is due to Magewell capture devices have proven to be unstable after the
   first recording attempt.
 
-  Args :
-    ref_video_device(string): reference recording device path.
-    test_video_device(string): test recording device path
+  Args:
+    ref_video_device_path(string): reference recording device path.
+    test_video_device_path(string): test recording device path
 
   Raises:
     MagewellError: If no magewell devices are found.
   """
 
   # Get the dev/videoN device name from the command line arguments.
-  ref_magewell = ref_video_device.split('/')[2]
-  test_magewell = test_video_device.split('/')[2]
-
-  # Find the device location including USB and USB Bus ID's.
-  device_string = '/sys/bus/usb/devices/usb*/**/**/video4linux/'
-  ref_magewell_device = glob.glob('%s%s' % (device_string, ref_magewell))
-  test_magewell_device = glob.glob('%s%s' % (device_string, test_magewell))
-
-  magewell_usb_ports = []
-
-  # Figure out the USB bus and port ID for each device.
-  ref_magewell_path = str(ref_magewell_device).split('/')
-  for directory in ref_magewell_path:
-    # Find the folder with pattern "N-N", e.g. "4-3" or \
-    # "[USB bus ID]-[USB port]"
-    if re.match(r'^\d-\d$', directory):
-      magewell_usb_ports.append(directory)
-
-  test_magewell_path = str(test_magewell_device).split('/')
-  for directory in test_magewell_path:
-    # Find the folder with pattern "N-N", e.g. "4-3" or \
-    # "[USB bus ID]-[USB port]"
-    if re.match(r'^\d-\d$', directory):
-      magewell_usb_ports.append(directory)
+  ref_magewell_path = ref_video_device_path.split('/')[2]
+  test_magewell_path = test_video_device_path.split('/')[2]
+  magewell_usb_ports = FindUsbPortForV4lDevices(ref_magewell_path,
+                                                test_magewell_path)
 
   # Abort early if no devices are found.
   if len(magewell_usb_ports) == 0: