[Intel-gfx] [PATCH] Fix intel_detect_pch() to work in xen environment.

[G.R.]

Hi guys,

In XEN HVM guest, there is always an emulated PIIX3 ISA bridge on slot 01.0.
This shadows the PCH ISA bridge on 1f.0 with the current
intel_detect_pch() implementation.
The issue can be easily solved by looping through all the ISA bridges
until the first match is found, instead of just check against the
first one.

Here I attach the patch I used locally. It's created on Torvalds's git.
Looking forward to your comments.

Thanks,
Timothy

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 530db83..3f7e5fb 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -408,9 +408,11 @@ void intel_detect_pch(struct drm_device *dev)
         * underneath. This is a requirement from virtualization team.
         */
        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;
+                       unsigned found = 1;
                        id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
                        dev_priv->pch_id = id;

@@ -440,10 +442,20 @@ void intel_detect_pch(struct drm_device *dev)
                                dev_priv->num_pch_pll = 0;
                                DRM_DEBUG_KMS("Found LynxPoint LP PCH\n");
                                WARN_ON(!IS_HASWELL(dev));
+                       } else {
+                               found = 0;
+                       }
+                       if (found) {
+                               BUG_ON(dev_priv->num_pch_pll > I915_NUM_PLLS);
+                               pci_dev_put(pch);
+                               break;
                        }
-                       BUG_ON(dev_priv->num_pch_pll > I915_NUM_PLLS);
                }
-               pci_dev_put(pch);
+               pch = pci_get_class(PCI_CLASS_BRIDGE_ISA << 8, curr);
+               pci_dev_put(curr);
+       }
+       if (!pch) {
+               DRM_DEBUG_KMS("No PCH found?\n");
        }
 }