[devices]: Add lpmode in sfputil.py for Accton AS7816 (sonic-net#2989)

Signed-off-by: brandon_chuang <brandon_chuang@edge-core.com>

device/accton/x86_64-accton_as7816_64x-r0/plugins/sfputil.py

@@ -2,6 +2,8 @@
 
 try:
     import time
+    import string
+    from ctypes import create_string_buffer
     from sonic_sfp.sfputilbase import SfpUtilBase 
 except ImportError, e:
     raise ImportError (str(e) + "- required module not found")
@@ -108,12 +110,6 @@ def reset(self, port_num):
         reg_file.write('1')
         reg_file.close()
         return True
-
-    def set_low_power_mode(self, port_nuM, lpmode):
-        raise NotImplementedError
-
-    def get_low_power_mode(self, port_num):
-        raise NotImplementedError
 
     def get_presence(self, port_num):
         # Check for invalid port_num
@@ -159,3 +155,61 @@ def get_transceiver_change_event(self):
         on this platform.
         """
         raise NotImplementedError
+
+    def get_low_power_mode(self, port_num):
+        # Check for invalid port_num
+        if port_num < self._port_start or port_num > self._port_end:
+            return False
+
+        try:
+            eeprom = None
+
+            if not self.get_presence(port_num):
+                return False
+
+            eeprom = open(self.port_to_eeprom_mapping[port_num], "rb")
+            eeprom.seek(93)
+            lpmode = ord(eeprom.read(1))
+
+            if ((lpmode & 0x3) == 0x3):
+                return True # Low Power Mode if "Power override" bit is 1 and "Power set" bit is 1
+            else:
+                return False # High Power Mode if one of the following conditions is matched:
+                             # 1. "Power override" bit is 0
+                             # 2. "Power override" bit is 1 and "Power set" bit is 0 
+        except IOError as e:
+            print "Error: unable to open file: %s" % str(e)
+            return False
+        finally:
+            if eeprom is not None:
+                eeprom.close()
+                time.sleep(0.01)
+
+    def set_low_power_mode(self, port_num, lpmode): 
+        # Check for invalid port_num
+        if port_num < self._port_start or port_num > self._port_end:
+            return False
+
+        try:
+            eeprom = None
+
+            if not self.get_presence(port_num):
+                return False # Port is not present, unable to set the eeprom
+
+            # Fill in write buffer
+            regval = 0x3 if lpmode else 0x1 # 0x3:Low Power Mode, 0x1:High Power Mode
+            buffer = create_string_buffer(1)
+            buffer[0] = chr(regval)
+
+            # Write to eeprom
+            eeprom = open(self.port_to_eeprom_mapping[port_num], "r+b")
+            eeprom.seek(93)
+            eeprom.write(buffer[0])
+            return True
+        except IOError as e:
+            print "Error: unable to open file: %s" % str(e)
+            return False
+        finally:
+            if eeprom is not None:
+                eeprom.close()
+                time.sleep(0.01)