Update discover to try and resolve a path to vcgencmd instead of …

…trying a hard-coded one

ovos_gui_plugin_shell_companion/brightness.py

@@ -5,7 +5,7 @@
 import time
 from datetime import timedelta
 from distutils.spawn import find_executable
-from os.path import isfile
+from os.path import isfile, exists
 from astral import LocationInfo
 from astral.sun import sun
 from ovos_bus_client import Message
@@ -75,10 +75,21 @@ def is_auto_dim_enabled(self, message=None):
 
     # Discover the brightness control device interface (HDMI / DSI) on the Raspberry PI
     def discover(self):
+        try:
+            vcgen_path = (subprocess.run(["which", "vcgencmd"], check=True,
+                                         capture_output=True).stdout.decode()
+                          .strip())
+        except subprocess.CalledProcessError:
+            vcgen_path = "/opt/vc/bin/vcgencmd" if (
+                exists("/opt/vc/bin/vcgencmd")) else None
+        if not vcgen_path:
+            LOG.info("Falling back to DSI interface")
+            self.device_interface = "DSI"
         try:
             LOG.info("Discovering brightness control device interface")
-            proc = subprocess.Popen(["/opt/vc/bin/vcgencmd",
-                                     "get_config", "display_default_lcd"], stdout=subprocess.PIPE)
+            proc = subprocess.Popen([vcgen_path,
+                                     "get_config", "display_default_lcd"],
+                                    stdout=subprocess.PIPE)
             if proc.stdout.read().decode("utf-8").strip() == "1":
                 self.device_interface = "DSI"
             else:
@@ -101,7 +112,8 @@ def discover(self):
 
                 if self.ddcutil_detected_bus:
                     proc_fetch_vcp = subprocess.Popen(
-                        ["/usr/bin/ddcutil", "getvcp", "known", "--bus", self.ddcutil_detected_bus],
+                        ["/usr/bin/ddcutil", "getvcp", "known", "--bus",
+                         self.ddcutil_detected_bus],
                         stdout=subprocess.PIPE)
                     # check the vcp output for the Brightness string and get its VCP code
                     for line in proc_fetch_vcp.stdout: