vfio/igd: Introduce x-igd-lpc option for LPC bridge ID quirk

The LPC bridge/Host bridge IDs quirk is also not dependent on legacy
mode. Recent Windows driver no longer depends on these IDs, as well as
Linux i915 driver, while UEFI GOP seems still needs them. Make it an
option to allow users enabling and disabling it as needed.

Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Tested-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Corvin Köhne <c.koehne@beckhoff.com>
Link: https://lore.kernel.org/qemu-devel/20250306180131.32970-10-tomitamoeko@gmail.com
[ clg: - Fixed spelling in vfio_probe_igd_config_quirk() ]
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/igd.c

@@ -560,13 +560,9 @@ bool vfio_probe_igd_config_quirk(VFIOPCIDevice *vdev, Error **errp)
             goto error;
         }
 
-        /* Enable OpRegion quirk */
+        /* Enable OpRegion and LPC bridge quirk */
         vdev->features |= VFIO_FEATURE_ENABLE_IGD_OPREGION;
-
-        /* Setup LPC bridge / Host bridge PCI IDs */
-        if (!vfio_pci_igd_setup_lpc_bridge(vdev, &err)) {
-            goto error;
-        }
+        vdev->features |= VFIO_FEATURE_ENABLE_IGD_LPC;
     } else if (vdev->igd_legacy_mode == ON_OFF_AUTO_ON) {
         error_setg(&err,
                    "Machine is not i440fx or assigned BDF is not 00:02.0");
@@ -579,6 +575,12 @@ bool vfio_probe_igd_config_quirk(VFIOPCIDevice *vdev, Error **errp)
         goto error;
     }
 
+    /* Setup LPC bridge / Host bridge PCI IDs */
+    if ((vdev->features & VFIO_FEATURE_ENABLE_IGD_LPC) &&
+        !vfio_pci_igd_setup_lpc_bridge(vdev, errp)) {
+        goto error;
+     }
+
     /*
      * Allow user to override dsm size using x-igd-gms option, in multiples of
      * 32MiB. This option should only be used when the desired size cannot be

hw/vfio/pci.c

@@ -3360,6 +3360,8 @@ static const Property vfio_pci_dev_properties[] = {
                     VFIO_FEATURE_ENABLE_REQ_BIT, true),
     DEFINE_PROP_BIT("x-igd-opregion", VFIOPCIDevice, features,
                     VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false),
+    DEFINE_PROP_BIT("x-igd-lpc", VFIOPCIDevice, features,
+                    VFIO_FEATURE_ENABLE_IGD_LPC_BIT, false),
     DEFINE_PROP_ON_OFF_AUTO("x-igd-legacy-mode", VFIOPCIDevice,
                             igd_legacy_mode, ON_OFF_AUTO_AUTO),
     DEFINE_PROP_ON_OFF_AUTO("enable-migration", VFIOPCIDevice,

hw/vfio/pci.h

@@ -154,6 +154,9 @@ struct VFIOPCIDevice {
 #define VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT 2
 #define VFIO_FEATURE_ENABLE_IGD_OPREGION \
                                 (1 << VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT)
+#define VFIO_FEATURE_ENABLE_IGD_LPC_BIT 3
+#define VFIO_FEATURE_ENABLE_IGD_LPC \
+                                (1 << VFIO_FEATURE_ENABLE_IGD_LPC_BIT)
     OnOffAuto display;
     uint32_t display_xres;
     uint32_t display_yres;