Workaround incoherence between fences and LLC across multiple CPUs

from linux 3.8.13

this does not currently do the ipi to run wbinvd() on all processors

1 files changed, 31 insertions, 6 deletions

diff --git a/sys/dev/pci/drm/i915/i915_gem.c b/sys/dev/pci/drm/i915/i915_gem.c
index 4fbc43047ec..6c15b56f2d8 100644
--- a/sys/dev/pci/drm/i915/i915_gem.c
+++ b/sys/dev/pci/drm/i915/i915_gem.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: i915_gem.c,v 1.25 2013/06/12 14:28:40 kettenis Exp $	*/
+/*	$OpenBSD: i915_gem.c,v 1.26 2013/07/04 09:49:00 jsg Exp $	*/
 /*
  * Copyright (c) 2008-2009 Owain G. Ainsworth <oga@openbsd.org>
  *
@@ -1925,18 +1925,43 @@ fence_number(drm_i915_private_t *dev_priv,
 	return fence - dev_priv->fence_regs;
 }
 
+#ifdef __linux__
+void
+i915_gem_write_fence__ipi(void *data)
+{
+	wbinvd();
+}
+#endif
+
 void
 i915_gem_object_update_fence(struct drm_i915_gem_object *obj,
 					 struct drm_i915_fence_reg *fence,
 					 bool enable)
 {
-	struct drm_i915_private *dev_priv = obj->base.dev->dev_private;
-	int reg = fence_number(dev_priv, fence);
-
-	i915_gem_write_fence(obj->base.dev, reg, enable ? obj : NULL);
+	struct drm_device *dev = obj->base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	int fence_reg = fence_number(dev_priv, fence);
+
+	/* In order to fully serialize access to the fenced region and
+	 * the update to the fence register we need to take extreme
+	 * measures on SNB+. In theory, the write to the fence register
+	 * flushes all memory transactions before, and coupled with the
+	 * mb() placed around the register write we serialise all memory
+	 * operations with respect to the changes in the tiler. Yet, on
+	 * SNB+ we need to take a step further and emit an explicit wbinvd()
+	 * on each processor in order to manually flush all memory
+	 * transactions before updating the fence register.
+	 */
+	if (HAS_LLC(obj->base.dev))
+#ifdef __linux__
+		on_each_cpu(i915_gem_write_fence__ipi, NULL, 1);
+#else
+		wbinvd();
+#endif
+	i915_gem_write_fence(dev, fence_reg, enable ? obj : NULL);
 
 	if (enable) {
-		obj->fence_reg = reg;
+		obj->fence_reg = fence_reg;
 		fence->obj = obj;
 		list_move_tail(&fence->lru_list, &dev_priv->mm.fence_list);
 	} else {