power/gpio: Allow to configure low level triggered relays

Introduce an optional `enable` config key for the power gpio. This
config defaults to `high` for high level triggered relays but can be
set to `low` for low level triggered relays.

Signed-off-by: Tobias Schaffner <tobias.schaffner@siemens.com>

docs/config.rst

@@ -262,10 +262,14 @@ supported:
     Format: <gpiochipx>@<pin>
     If multiple GPIO lines and pins are used separate the entries using ','.
 
+* ``enable``: string [optional]
+    If the relay enable trigger is ``high`` or ``low``. Defaults to ``high``.
+
     Example::
 
         # For single GPIO line
         gpio = gpiochip0@201
+        enable = high
         # For multiple GPIO lines
         gpio = gpiochip0@201,gpiochip1@11,gpiochip0@203
 

mtda.ini

@@ -132,7 +132,8 @@ time-until = login:
 variant=aviosys_8800
 
 # variant=gpio
-# pins=48
+# gpio=gpiochip0@203
+# enable=high
 
 # variant=pduclient
 # daemon=134.86.60.40

mtda/power/gpio.py

@@ -19,17 +19,29 @@
 
 class GpioPowerController(PowerController):
 
+    HIGH = 1
+    LOW = 0
+
     def __init__(self, mtda):
         self.dev = None
         self.mtda = mtda
         self.lines = []
         self.gpiopair = []
+        self.trigger = self.HIGH
 
     def configure(self, conf):
         self.mtda.debug(3, "power.gpio.configure()")
 
         result = None
 
+        if 'enable' in conf:
+            if conf['enable'] == 'high':
+                self.trigger = self.HIGH
+            elif conf['enable'] == 'low':
+                self.trigger = self.LOW
+            else:
+                raise ValueError("'enable' shall be either 'high' or 'low'!")
+
         if 'gpio' in conf:
             for gpio in conf['gpio'].split(','):
                 self.gpiopair.append(itemgetter(0, 1)(gpio.split('@')))
@@ -83,7 +95,7 @@ def on(self):
         result = False
 
         for line in self.lines:
-            line.set_value(1)
+            line.set_value(self.trigger)
         result = self.status() == self.POWER_ON
 
         self.mtda.debug(3, f"power.gpio.on(): {result}")
@@ -95,7 +107,7 @@ def off(self):
         result = False
 
         for line in self.lines:
-            line.set_value(0)
+            line.set_value(self.trigger ^ 1)
         result = self.status() == self.POWER_OFF
 
         self.mtda.debug(3, f"power.gpio.off(): {result}")
@@ -109,7 +121,7 @@ def status(self):
 
         for line in self.lines:
             value = line.get_value()
-            if value == 1:
+            if value == self.trigger:
                 value = self.POWER_ON
             else:
                 value = self.POWER_OFF