drm/i915: Fix PCH detect with multiple ISA bridges in VM

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.
Signed-off-by: Rui Guo <firemeteor@users.sourceforge.net>
[danvet: Fixup conflict with the num_pch_pll removal. And add
subsystem header to the commit message headline.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

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;
+		}
+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)