[PATCH] drm/i915: refine qemu south bridge detection

[Gerd Hoffmann <kraxel@redhat.com>]

The test for the qemu q35 south bridge added by commit
"39bfcd52 drm/i915: more virtual south bridge detection"
also matches on real hardware.  Having the check for
virtual systems last in the list is not enough to avoid
that ...

Refine the check by additionally verifying the pci
subsystem id to see whenever it *really* is qemu.

Reported-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 drivers/gpu/drm/i915/i915_drv.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 3ac616d..9668162 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -501,7 +501,9 @@ void intel_detect_pch(struct drm_device *dev)
 				WARN_ON(!IS_SKYLAKE(dev) &&
 					!IS_KABYLAKE(dev));
 			} else if ((id == INTEL_PCH_P2X_DEVICE_ID_TYPE) ||
-				   (id == INTEL_PCH_QEMU_DEVICE_ID_TYPE)) {
+				   ((id == INTEL_PCH_QEMU_DEVICE_ID_TYPE) &&
+				    pch->subsystem_vendor == 0x1a4f &&
+				    pch->subsystem_device == 0x1100)) {
 				dev_priv->pch_type = intel_virt_detect_pch(dev);
 			} else
 				continue;
-- 
1.8.3.1