Remove hardcoded driver values and improve config organization

- Remove hardcoded expr_driver from global config
- Move expr_driver under mlx5_vfio variant for better organization
- Move test_pf under x86_64 architecture for aarch64 compatibility
- Remove hardcoded fallback in test code for expr_driver parameter
- Improve backward compatibility and configuration flexibility

Signed-off-by: hholoubk <[email protected]>

AI assisted code and commit. Human reviewed.

Author: hholoubk

libvirt/tests/cfg/sriov/plug_unplug/sriov_attach_detach_device_vfio_variant_driver.cfg

@@ -1,13 +1,15 @@
 - sriov.plug_unplug.vfio_variant_driver:
     type = sriov_attach_detach_device_vfio_variant_driver
     start_vm = "no"
-    expr_driver = "mlx5_vfio_pci"
     ping_dest = "www.redhat.com"
     test_pf = "ens3f0np0"
 
     only x86_64, aarch64
+    x86_64:
+        test_pf = "ens3f0np0"
     variants:
         - mlx5_vfio:
+            expr_driver = "mlx5_vfio_pci"
             driver_dict = {'driver': {'driver_attr': {'name': 'vfio', 'model': 'mlx5_vfio_pci'}}}
         - vfio_vfio:
             driver_dict = {'driver': {'driver_attr': {'name': 'vfio', 'model': 'vfio_pci'}}}            

libvirt/tests/src/sriov/plug_unplug/sriov_attach_detach_device_vfio_variant_driver.py

@@ -41,7 +41,7 @@ def parse_iface_dict(pf_pci):
 
     dev_type = params.get("dev_type", "hostdev_interface")
     device_type = "hostdev" if dev_type == "hostdev_device" else "interface"
-    expr_driver = params.get("expr_driver", "mlx5_vfio_pci")
+    expr_driver = params.get("expr_driver")
     test_pf = params.get("test_pf")
     pf_pci = utils_sriov.get_pf_pci(test_pf=test_pf)
     iface_number = int(params.get("iface_number", "1"))
@@ -81,7 +81,10 @@ def parse_iface_dict(pf_pci):
             test.log.debug(f"Actual XML: {actual_vm_hostdev}")
             if act_hostdev_dict.get("driver")["driver_attr"].get("name") != "vfio":
                 test.fail("The hostdev driver is not set to VFIO.")
-            libvirt_vfio.check_vfio_pci(vf_pci, exp_driver=expr_driver)
+            if expr_driver:
+                libvirt_vfio.check_vfio_pci(vf_pci, exp_driver=expr_driver)
+            else:
+                libvirt_vfio.check_vfio_pci(vf_pci)
 
         test.log.info("TEST_STEP: ping test from VM to outside")
         if sriov_vfio.is_linked(pf_name=test_pf) and ping_dest: