1 files changed, 16 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index deaa32e8113b..062cbda1bf4a 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -465,9 +465,15 @@ void intel_detect_pch(struct drm_device *dev)
          * make graphics device passthrough work easy for VMM, that only
          * need to expose ISA bridge to let driver know the real hardware
          * underneath. This is a requirement from virtualization team.
+         *
+         * In some virtualized environments (e.g. XEN), there is irrelevant
+         * ISA bridge in the system. To work reliably, we should scan trhough
+         * all the ISA bridge devices and check for the first match, instead
+         * of only checking the first one.
          */
         pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, NULL);
-        if (pch) {
+        while (pch) {
+                struct pci_dev *curr = pch;
                 if (pch->vendor == PCI_VENDOR_ID_INTEL) {
                         unsigned short id;
                         id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
@@ -496,10 +502,18 @@ void intel_detect_pch(struct drm_device *dev)
                                 DRM_DEBUG_KMS("Found LynxPoint LP PCH\n");
                                 WARN_ON(!IS_HASWELL(dev));
                                 WARN_ON(!IS_ULT(dev));
+                        } else {
+                                goto check_next;
                         }
+                        pci_dev_put(pch);
+                        break;
                 }
-                pci_dev_put(pch);
+check_next:
+                pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, curr);
+                pci_dev_put(curr);
         }
+        if (!pch)
+                DRM_DEBUG_KMS("No PCH found?\n");
 }
 
 bool i915_semaphore_is_enabled(struct drm_device *dev)