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

[firemeteor at users.sourceforge.net (G.R.)]

On Sun, Dec 23, 2012 at 2:51 PM, G.R. <firemeteor at users.sourceforge.net> wrote:
>>> Hi Jesse, I think I need to resend the patch with proper comment to
>>> have it formally accepted.
>>> Any guide line for formal patch submission? Do I need to start a
>>> separate thread?
>>
>> No, just cc Daniel Vetter.
>>
>> --
>> Jesse Barnes, Intel Open Source Technology Center
>
> Thanks,
> Resend with updated patch && Daniel involved.
> Also include the background info for easy reading.
>
> 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.
>

This seems to have lost in the list. Retry it again with latest
torvalds' kernel:

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index a2e4953..e38fa86 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -454,11 +454,18 @@ 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;
+                       unsigned found = 1;
                        id = pch->device & INTEL_PCH_DEVICE_ID_MASK;
                        dev_priv->pch_id = id;

@@ -490,10 +497,20 @@ 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 {
+                               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");
        }
 }