drm/i915: Disable GGTT PTEs on GEN6+ suspend

Once the machine gets to a certain point in the suspend process, we
expect the GPU to be idle. If it is not, we might corrupt memory.
Empirically (with an early version of this patch) we have seen this is
not the case. We cannot currently explain why the latent GPU writes
occur.

In the technical sense, this patch is a workaround in that we have an
issue we can't explain, and the patch indirectly solves the issue.
However, it's really better than a workaround because we understand why
it works, and it really should be a safe thing to do in all cases.

The noticeable effect other than the debug messages would be an increase
in the suspend time. I have not measure how expensive it actually is.

I think it would be good to spend further time to root cause why we're
seeing these latent writes, but it shouldn't preclude preventing the
fallout.

NOTE: It should be safe (and makes some sense IMO) to also keep the
VALID bit unset on resume when we clear_range(). I've opted not to do
this as properly clearing those bits at some later point would be extra
work.

v2: Fix bugzilla link

Bugzilla: http://bugs.freedesktop.org/show_bug.cgi?id=65496
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=59321
Tested-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Tested-By: Todd Previte <tprevite@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 66 insertions, 10 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 32aa69d7ef20..1f7b4caefb6e 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -241,7 +241,8 @@ static int gen6_ppgtt_enable(struct drm_device *dev)
 /* PPGTT support for Sandybdrige/Gen6 and later */
 static void gen6_ppgtt_clear_range(struct i915_address_space *vm,
 				   unsigned first_entry,
-				   unsigned num_entries)
+				   unsigned num_entries,
+				   bool use_scratch)
 {
 	struct i915_hw_ppgtt *ppgtt =
 		container_of(vm, struct i915_hw_ppgtt, base);
@@ -372,7 +373,7 @@ static int gen6_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 	}
 
 	ppgtt->base.clear_range(&ppgtt->base, 0,
-				ppgtt->num_pd_entries * I915_PPGTT_PT_ENTRIES);
+				ppgtt->num_pd_entries * I915_PPGTT_PT_ENTRIES, true);
 
 	ppgtt->pd_offset = first_pd_entry_in_global_pt * sizeof(gen6_gtt_pte_t);
 
@@ -449,7 +450,8 @@ void i915_ppgtt_unbind_object(struct i915_hw_ppgtt *ppgtt,
 {
 	ppgtt->base.clear_range(&ppgtt->base,
 				i915_gem_obj_ggtt_offset(obj) >> PAGE_SHIFT,
-				obj->base.size >> PAGE_SHIFT);
+				obj->base.size >> PAGE_SHIFT,
+				true);
 }
 
 extern int intel_iommu_gfx_mapped;
@@ -490,15 +492,65 @@ static void undo_idling(struct drm_i915_private *dev_priv, bool interruptible)
 		dev_priv->mm.interruptible = interruptible;
 }
 
+void i915_check_and_clear_faults(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct intel_ring_buffer *ring;
+	int i;
+
+	if (INTEL_INFO(dev)->gen < 6)
+		return;
+
+	for_each_ring(ring, dev_priv, i) {
+		u32 fault_reg;
+		fault_reg = I915_READ(RING_FAULT_REG(ring));
+		if (fault_reg & RING_FAULT_VALID) {
+			DRM_DEBUG_DRIVER("Unexpected fault\n"
+					 "\tAddr: 0x%08lx\\n"
+					 "\tAddress space: %s\n"
+					 "\tSource ID: %d\n"
+					 "\tType: %d\n",
+					 fault_reg & PAGE_MASK,
+					 fault_reg & RING_FAULT_GTTSEL_MASK ? "GGTT" : "PPGTT",
+					 RING_FAULT_SRCID(fault_reg),
+					 RING_FAULT_FAULT_TYPE(fault_reg));
+			I915_WRITE(RING_FAULT_REG(ring),
+				   fault_reg & ~RING_FAULT_VALID);
+		}
+	}
+	POSTING_READ(RING_FAULT_REG(&dev_priv->ring[RCS]));
+}
+
+void i915_gem_suspend_gtt_mappings(struct drm_device *dev)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	/* Don't bother messing with faults pre GEN6 as we have little
+	 * documentation supporting that it's a good idea.
+	 */
+	if (INTEL_INFO(dev)->gen < 6)
+		return;
+
+	i915_check_and_clear_faults(dev);
+
+	dev_priv->gtt.base.clear_range(&dev_priv->gtt.base,
+				       dev_priv->gtt.base.start / PAGE_SIZE,
+				       dev_priv->gtt.base.total / PAGE_SIZE,
+				       false);
+}
+
 void i915_gem_restore_gtt_mappings(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_i915_gem_object *obj;
 
+	i915_check_and_clear_faults(dev);
+
 	/* First fill our portion of the GTT with scratch pages */
 	dev_priv->gtt.base.clear_range(&dev_priv->gtt.base,
 				       dev_priv->gtt.base.start / PAGE_SIZE,
-				       dev_priv->gtt.base.total / PAGE_SIZE);
+				       dev_priv->gtt.base.total / PAGE_SIZE,
+				       true);
 
 	list_for_each_entry(obj, &dev_priv->mm.bound_list, global_list) {
 		i915_gem_clflush_object(obj, obj->pin_display);
@@ -565,7 +617,8 @@ static void gen6_ggtt_insert_entries(struct i915_address_space *vm,
 
 static void gen6_ggtt_clear_range(struct i915_address_space *vm,
 				  unsigned int first_entry,
-				  unsigned int num_entries)
+				  unsigned int num_entries,
+				  bool use_scratch)
 {
 	struct drm_i915_private *dev_priv = vm->dev->dev_private;
 	gen6_gtt_pte_t scratch_pte, __iomem *gtt_base =
@@ -578,7 +631,8 @@ static void gen6_ggtt_clear_range(struct i915_address_space *vm,
 		 first_entry, num_entries, max_entries))
 		num_entries = max_entries;
 
-	scratch_pte = vm->pte_encode(vm->scratch.addr, I915_CACHE_LLC, true);
+	scratch_pte = vm->pte_encode(vm->scratch.addr, I915_CACHE_LLC, use_scratch);
+
 	for (i = 0; i < num_entries; i++)
 		iowrite32(scratch_pte, &gtt_base[i]);
 	readl(gtt_base);
@@ -599,7 +653,8 @@ static void i915_ggtt_insert_entries(struct i915_address_space *vm,
 
 static void i915_ggtt_clear_range(struct i915_address_space *vm,
 				  unsigned int first_entry,
-				  unsigned int num_entries)
+				  unsigned int num_entries,
+				  bool unused)
 {
 	intel_gtt_clear_range(first_entry, num_entries);
 }
@@ -627,7 +682,8 @@ void i915_gem_gtt_unbind_object(struct drm_i915_gem_object *obj)
 
 	dev_priv->gtt.base.clear_range(&dev_priv->gtt.base,
 				       entry,
-				       obj->base.size >> PAGE_SHIFT);
+				       obj->base.size >> PAGE_SHIFT,
+				       true);
 
 	obj->has_global_gtt_mapping = 0;
 }
@@ -714,11 +770,11 @@ void i915_gem_setup_global_gtt(struct drm_device *dev,
 		const unsigned long count = (hole_end - hole_start) / PAGE_SIZE;
 		DRM_DEBUG_KMS("clearing unused GTT space: [%lx, %lx]\n",
 			      hole_start, hole_end);
-		ggtt_vm->clear_range(ggtt_vm, hole_start / PAGE_SIZE, count);
+		ggtt_vm->clear_range(ggtt_vm, hole_start / PAGE_SIZE, count, true);
 	}
 
 	/* And finally clear the reserved guard page */
-	ggtt_vm->clear_range(ggtt_vm, end / PAGE_SIZE - 1, 1);
+	ggtt_vm->clear_range(ggtt_vm, end / PAGE_SIZE - 1, 1, true);
 }
 
 static bool