drm/i915: disable ppgtt on snb when dmar is enabled

Totally unexpected that this regressed. Luckily it sounds like we just
need to have dmar disable on the igfx, not the entire system. At least
that's what a few days of testing between Tony Vroon and me indicates.

Reported-by: Tony Vroon <tony@linx.net>
Cc: Tony Vroon <tony@linx.net>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=43024
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/char/agp/intel-gtt.c

@@ -1190,7 +1190,6 @@ static inline int needs_idle_maps(void)
 {
 #ifdef CONFIG_INTEL_IOMMU
 	const unsigned short gpu_devid = intel_private.pcidev->device;
-	extern int intel_iommu_gfx_mapped;
 
 	/* Query intel_iommu to see if we need the workaround. Presumably that
 	 * was loaded first.

drivers/gpu/drm/i915/i915_dma.c

@@ -1183,6 +1183,21 @@ static bool i915_switcheroo_can_switch(struct pci_dev *pdev)
 	return can_switch;
 }
 
+static bool
+intel_enable_ppgtt(struct drm_device *dev)
+{
+	if (i915_enable_ppgtt >= 0)
+		return i915_enable_ppgtt;
+
+#ifdef CONFIG_INTEL_IOMMU
+	/* Disable ppgtt on SNB if VT-d is on. */
+	if (INTEL_INFO(dev)->gen == 6 && intel_iommu_gfx_mapped)
+		return false;
+#endif
+
+	return true;
+}
+
 static int i915_load_gem_init(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -1197,7 +1212,7 @@ static int i915_load_gem_init(struct drm_device *dev)
 	drm_mm_init(&dev_priv->mm.stolen, 0, prealloc_size);
 
 	mutex_lock(&dev->struct_mutex);
-	if (i915_enable_ppgtt && HAS_ALIASING_PPGTT(dev)) {
+	if (intel_enable_ppgtt(dev) && HAS_ALIASING_PPGTT(dev)) {
 		/* PPGTT pdes are stolen from global gtt ptes, so shrink the
 		 * aperture accordingly when using aliasing ppgtt. */
 		gtt_size -= I915_PPGTT_PD_ENTRIES*PAGE_SIZE;

drivers/gpu/drm/i915/i915_drv.c

@@ -107,8 +107,8 @@ MODULE_PARM_DESC(enable_hangcheck,
 		"WARNING: Disabling this can cause system wide hangs. "
 		"(default: true)");
 
-bool i915_enable_ppgtt __read_mostly = 1;
-module_param_named(i915_enable_ppgtt, i915_enable_ppgtt, bool, 0600);
+int i915_enable_ppgtt __read_mostly = -1;
+module_param_named(i915_enable_ppgtt, i915_enable_ppgtt, int, 0600);
 MODULE_PARM_DESC(i915_enable_ppgtt,
 		"Enable PPGTT (default: true)");
 

drivers/gpu/drm/i915/i915_drv.h

@@ -1086,7 +1086,7 @@ extern int i915_vbt_sdvo_panel_type __read_mostly;
 extern int i915_enable_rc6 __read_mostly;
 extern int i915_enable_fbc __read_mostly;
 extern bool i915_enable_hangcheck __read_mostly;
-extern bool i915_enable_ppgtt __read_mostly;
+extern int i915_enable_ppgtt __read_mostly;
 
 extern int i915_suspend(struct drm_device *dev, pm_message_t state);
 extern int i915_resume(struct drm_device *dev);

include/drm/intel-gtt.h

@@ -44,4 +44,8 @@ void intel_gtt_insert_pages(unsigned int first_entry, unsigned int num_entries,
 /* flag for GFDT type */
 #define AGP_USER_CACHED_MEMORY_GFDT (1 << 3)
 
+#ifdef CONFIG_INTEL_IOMMU
+extern int intel_iommu_gfx_mapped;
+#endif
+
 #endif