[Mellanox] Extend Nvidia Bluefield DPU chassis implementation (sonic-net#20620)

- Why I did it
Implement the interface required to run DPU chassisd on the Nvidia Smart Switch.
Implement get_dpu_id API that deducts the DPU ID based on the midplane interface IP address.

- How I did it
Implement platform API

- How to verify it
The implementation is covered by the UT.

Author: oleksandrivantsiv

device/nvidia-bluefield/arm64-nvda_bf-bf3comdpu/pmon_daemon_control.json

@@ -2,6 +2,6 @@
     "skip_ledd": true,
     "skip_psud": true,
     "skip_fancontrol": true,
-    "skip_chassisd": true,
+    "skip_chassisd": false,
     "skip_ycabled": true
 }

platform/nvidia-bluefield/platform-api/sonic_platform/chassis.py

@@ -22,6 +22,9 @@
     import os
     from functools import reduce
     from time import sleep
+    import psutil
+    import ipaddress
+    import socket
 
     from . import utils
     from .device_data import DeviceDataManager
@@ -53,8 +56,25 @@ def __init__(self):
         self.sfp_event = None
         self._eeprom = Eeprom()
         self._watchdog = Watchdog()
+
         logger.log_info("Chassis loaded successfully")
 
+    def _get_dpu_id(self):
+        ip = None
+        midplane_inft = psutil.net_if_addrs().get('eth0-midplane', [])
+
+        for address in midplane_inft:
+            if address.family == socket.AF_INET:
+                ip = ipaddress.IPv4Address(address.address)
+                break
+
+        if not ip:
+            raise RuntimeError("Midplane interface IP address is not available")
+
+        last_byte = int(str(ip).split('.')[-1])
+
+        return last_byte - 1
+
     def _initialize_sfp(self):
         self._sfp_list = []
 
@@ -272,3 +292,36 @@ def get_reboot_cause(self):
             to pass a description of the reboot cause.
         """
         return "N/A", "N/A"
+
+    ##############################################
+    # SmartSwitch methods
+    ##############################################
+
+    def get_dpu_id(self, **kwargs):
+        """
+        For the smart switch DPU retrieves the ID of the DPU.
+        Returns None for non-smartswitch chassis.
+
+        Returns:
+            An integer, indicating the DPU ID Ex: name:DPU0 return value 0,
+            name:DPU1 return value 1, name:DPUX return value X
+        """
+        return self._get_dpu_id()
+
+    def is_smartswitch(self):
+        """
+        Retrieves whether the sonic instance is part of smartswitch
+
+        Returns:
+            Returns:True for SmartSwitch and False for other platforms
+        """
+        return True
+
+    def is_dpu(self):
+        """
+        Retrieves whether the SONiC instance runs on the DPU
+
+        Returns:
+            True if the SONiC instance runs on the DPU else False
+        """
+        return True

platform/nvidia-bluefield/platform-api/tests/test_chassis.py

@@ -17,6 +17,8 @@
 
 import os
 import sys
+import socket
+from collections import namedtuple
 
 from unittest.mock import patch
 from unittest.mock import mock_open
@@ -83,3 +85,11 @@ def test_sfp(self, *args):
         assert len(sfp_list) == 2
         assert id(sfp1) == id(sfp_list[0])
         assert id(sfp2) == id(sfp_list[1])
+
+
+    @patch('psutil.net_if_addrs', return_value={
+        'eth0-midplane': [namedtuple('snicaddr', ['family', 'address'])(family=socket.AF_INET, address='169.254.200.1')]})
+    def test_get_dpu_id(self, *args):
+        chassis = Chassis()
+
+        assert chassis.get_dpu_id() == 0