[devices]: Add lpmode in sfputil.py for Accton AS7312-54XS (#3007)

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

device/accton/x86_64-accton_as7312_54xs-r0/plugins/sfputil.py

@@ -5,6 +5,8 @@
 
 try:
     import time
+    import string
+    from ctypes import create_string_buffer
     from sonic_sfp.sfputilbase import SfpUtilBase
 except ImportError as e:
     raise ImportError("%s - required module not found" % str(e))
@@ -187,10 +189,62 @@ class SfpUtil(SfpUtilBase):
         return False
 
     def get_low_power_mode(self, port_num):
-        raise NotImplementedError
+        # Check for invalid port_num
+        if port_num < self.qsfp_port_start or port_num > self.qsfp_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): 
-        raise NotImplementedError
+        # Check for invalid port_num
+        if port_num < self.qsfp_port_start or port_num > self.qsfp_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)
 
     def reset(self, port_num):
         if port_num < self.qsfp_port_start or port_num > self.qsfp_port_end: