[Mellanox] Fix timing issue in lpmode change

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

@@ -26,6 +26,7 @@
     import ctypes
     import subprocess
     import os
+    import time
     import threading
     from sonic_py_common.logger import Logger
     from sonic_py_common.general import check_output_pipe
@@ -620,6 +621,18 @@ def _set_lpmode_raw(cls, sdk_handle, sdk_index, slot_id, ports, attr_type, power
 
         return result
 
+    def check_lpmode(self, desired_lpmode, api):
+        return api.get_lpmode() == desired_lpmode
+
+
+    def wait_until(self, timeout, poll_interval, desired_lpmode, api):
+        start_time = time.time()
+        while not self.check_lpmode(desired_lpmode, api):
+            if time.time() - start_time >= timeout:
+                return False
+            time.sleep(poll_interval)
+        return True
+
 
     def set_lpmode(self, lpmode):
         """
@@ -640,7 +653,7 @@ def set_lpmode(self, lpmode):
                 if api.get_lpmode() == lpmode:
                     return True
                 api.set_lpmode(lpmode)
-                return api.get_lpmode() == lpmode
+                return self.wait_until(timeout=2, poll_interval=0.5, desired_lpmode=lpmode, api=api)
             elif DeviceDataManager.is_independent_mode():
                 # FW control under CMIS host management mode. 
                 # Currently, we don't support set LPM under this mode.