[Mellanox] Fix issue: sfp.get_temperature_info cannot detect SFP replacement

platform/mellanox/mlnx-platform-api/sonic_platform/sfp.py

@@ -847,13 +847,27 @@ def get_tx_fault(self):
             print(e)
         return [False] * api.NUM_CHANNELS if api else None
 
+    def _get_serial(self):
+        """
+        Get serial number from EEPROM. sfp_base.get_serial() might read from
+        memory cache, which is not always up to date. This function is used by reinit_if_sn_changed() to detect if a SFP is replaced.
+        """
+        api = self.get_xcvr_api()
+        if not api:
+            return None
+
+        sn = api.xcvr_eeprom.read(consts.VENDOR_SERIAL_NO_FIELD)
+        if sn is None:
+            return None
+        return sn.rstrip()
+
     def reinit_if_sn_changed(self):
         """Reinitialize the SFP if the module ID has changed
         """
-        sn = self.get_serial()
+        sn = self._get_serial()
         if sn != self.sn:
             self.reinit()
-            self.sn = self.get_serial()
+            self.sn = self._get_serial()
             self.temp_high_threshold = None
             self.temp_critical_threshold = None
             return True

platform/mellanox/mlnx-platform-api/tests/test_sfp.py

@@ -607,3 +607,15 @@ def mock_read(field):
         assert sfp.get_temperature_info() == (True, 58.0, 75.0, 85.0)
         sfp.is_sw_control.side_effect = Exception('')
         assert sfp.get_temperature_info() == (False, None, None, None)
+
+    def test_reinit_if_sn_changed(self):
+        sfp = SFP(0)
+        sfp.get_xcvr_api = mock.MagicMock(return_value=None)
+        assert not sfp.reinit_if_sn_changed()
+
+        sfp.get_xcvr_api.return_value = mock.MagicMock()
+        sfp.get_xcvr_api.return_value.xcvr_eeprom.read = mock.MagicMock(return_value='1234567890')
+        assert sfp.reinit_if_sn_changed()
+
+        sfp.get_xcvr_api.return_value.xcvr_eeprom.read.return_value = '1234567891'
+        assert sfp.reinit_if_sn_changed()