Add a template function that returns list of asics on module (sonic-n…

…et#185)

Add a generic function that returns a list of asics on module. Vendors will implement their own for their platform.

The function could be used for collecting fabric asic info in each module and populating into CHASSIS_STATE_DB (sonic-net/sonic-platform-daemons#175). To simplify the change, all fabric cards in system should be identical in terms of number of asics in a card.

sonic_platform_base/module_base.py

@@ -71,6 +71,10 @@ def __init__(self):
         # available on the module
         self._sfp_list = []
 
+        # List of ASIC-derived objects representing all ASICs
+        # visibile in PCI domain on the module
+        self._asic_list = []
+
     def get_base_mac(self):
         """
         Retrieves the base MAC address for the module
@@ -461,4 +465,34 @@ def is_midplane_reachable(self):
         Returns:
             A bool value, should return True if module is reachable via midplane
         """
-        raise NotImplementedError
+        return NotImplementedError
+
+    ##############################################
+    # ASIC methods
+    ##############################################
+    def get_all_asics(self):
+        """
+        Retrieves the list of all ASICs on the module that are visible in PCI domain.
+        When called from the Supervisor of modular system, the module could be
+        fabric card, and the function returns all fabric ASICs on this module that
+        appear in PCI domain of the Supervisor.
+
+        Returns:
+            A list of ASICs. Index of an ASIC in the list is the index of the ASIC
+            on the module. Index is 0 based.
+
+            An item in the list is a tuple that includes:
+               - ASIC instance number (indexed globally across all modules of
+                 the chassis). This number is used to find settings for the ASIC
+                 from /usr/share/sonic/device/platform/hwsku/asic_instance_number/.
+               - ASIC PCI address: It is used by syncd to attach the correct ASIC.
+
+            For example: [('4', '0000:05:00.0'), ('5', '0000:07:00.0')]
+               In this example, from the output, we know the module has 2 ASICs.
+               Item ('4', '0000:05:00.0') describes information about the first ASIC
+               in the module.
+               '4' means it is asic4 in the chassis. Settings for this ASIC is at
+               /usr/share/sonic/device/platform/hwsku/4/.
+               And '0000:05:00.0' is its PCI address.
+        """
+        return self._asic_list