car_helpers: add variable to disable FW cache (#28626)

* Update car_helpers.py

* actually caches the fw

* simpler

selfdrive/car/car_helpers.py

@@ -79,6 +79,7 @@ interfaces = load_interfaces(interface_names)
 def fingerprint(logcan, sendcan, num_pandas):
   fixed_fingerprint = os.environ.get('FINGERPRINT', "")
   skip_fw_query = os.environ.get('SKIP_FW_QUERY', False)
+  disable_fw_cache = os.environ.get('DISABLE_FW_CACHE', False)
   ecu_rx_addrs = set()
   params = Params()
 
@@ -92,7 +93,8 @@ def fingerprint(logcan, sendcan, num_pandas):
       if cached_params.carName == "mock":
         cached_params = None
 
-    if cached_params is not None and len(cached_params.carFw) > 0 and cached_params.carVin is not VIN_UNKNOWN:
+    if cached_params is not None and len(cached_params.carFw) > 0 and \
+       cached_params.carVin is not VIN_UNKNOWN and not disable_fw_cache:
       cloudlog.warning("Using cached CarParams")
       vin, vin_rx_addr = cached_params.carVin, 0
       car_fw = list(cached_params.carFw)