Implementing dynamic device modules

Dynamic modules may be loaded automatically on device initialization if
the device supports them. Dynamic modules implent probe() method to
determine whether they are supported by a particular deviced.

devcpufreq and cpuidle have been converted into dynamic modules

wlauto/modules/cpufreq.py

@@ -28,6 +28,10 @@ class CpufreqModule(Module):
     """
     capabilities = ['cpufreq']
 
+    def probe(self, device):  # pylint: disable=no-self-use
+        path = '/sys/devices/system/cpu/cpufreq'
+        return device.file_exists(path)
+
     def initialize(self, context):
         # pylint: disable=W0201
         CpufreqModule._available_governors = {}

wlauto/modules/cpuidle.py

@@ -86,6 +86,9 @@ class Cpuidle(Module):
 
     root_path = '/sys/devices/system/cpu/cpuidle'
 
+    def probe(self, device):
+        return device.file_exists(self.root_path)
+
     def initialize(self, context):
         self.device = self.root_owner
         signal.connect(self._on_device_init, signal.RUN_INIT, priority=1)