As the presence of OpRegion is used to detect IGD device now, and
guest driver usually depends on OpRegion to work. Enable OpRegion
on IGD devices by default for out-of-the-box passthrough experience
(except pre-boot display output), especially for libvirt users.

Example of IGD passthrough with libvirt:
<hostdev mode="subsystem" type="pci" managed="yes">
  <source>
    <address domain="0x0000" bus="0x00" slot="0x02" function="0x0"/>
  </source>
  <rom file="/path/to/igd/rom"/>
  <address type="pci" domain="0x0000" bus="0x00" slot="0x02" function="0x0"/>
 </hostdev>

Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
---
 hw/vfio/pci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 05a7a62204..38ff231625 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -3361,7 +3361,7 @@ static const Property vfio_pci_dev_properties[] = {
     DEFINE_PROP_BIT("x-req", VFIOPCIDevice, features,
                     VFIO_FEATURE_ENABLE_REQ_BIT, true),
     DEFINE_PROP_BIT("x-igd-opregion", VFIOPCIDevice, features,
-                    VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, false),
+                    VFIO_FEATURE_ENABLE_IGD_OPREGION_BIT, true),
     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,
-- 
2.47.2