drm/i915: One hopeful eviction on PPGTT alloc

The patch before this changed the way in which we allocate space for the
PPGTT PDEs. It began carving out the PPGTT PDEs (which live in the
Global GTT) from the GGTT's drm_mm. Prior to that patch, the PDEs were
hidden from the drm_mm, and therefore could never fail to be allocated.

In unfortunate cases, the drm_mm may be full when we want to allocate
the space. This can technically occur whenever we try to allocate, which
happens in two places currently. Practically, it can only really ever
happen at GPU reset.

Later, when we allocate more PDEs for multiple PPGTTs this will
potentially even more useful.
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -640,6 +640,7 @@ static int gen6_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 #define GEN6_PD_SIZE (GEN6_PPGTT_PD_ENTRIES * PAGE_SIZE)
 	struct drm_device *dev = ppgtt->base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
+	bool retried = false;
 	int i, ret;
 
 	/* PPGTT PDEs reside in the GGTT and consists of 512 entries. The
@@ -647,14 +648,23 @@ static int gen6_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
 	 * size. We allocate at the top of the GTT to avoid fragmentation.
 	 */
 	BUG_ON(!drm_mm_initialized(&dev_priv->gtt.base.mm));
+alloc:
 	ret = drm_mm_insert_node_in_range_generic(&dev_priv->gtt.base.mm,
 						  &ppgtt->node, GEN6_PD_SIZE,
 						  GEN6_PD_ALIGN, 0,
 						  0, dev_priv->gtt.base.total,
 						  DRM_MM_SEARCH_DEFAULT);
+	if (ret == -ENOSPC && !retried) {
+		ret = i915_gem_evict_something(dev, &dev_priv->gtt.base,
+					       GEN6_PD_SIZE, GEN6_PD_ALIGN,
+					       I915_CACHE_NONE, false, true);
 		if (ret)
 			return ret;
 
+		retried = true;
+		goto alloc;
+	}
+
 	if (ppgtt->node.start < dev_priv->gtt.mappable_end)
 		DRM_DEBUG("Forced to use aperture for PDEs\n");