[PATCH 3/4] drm/i915: adjust fence registers asynchronously on tiling changes

[Daniel Vetter <daniel.vetter@ffwll.ch>]

This avoids stalling on the gpu. With the preparation from the
previous patch, this is really just a small change.

Thanks to Owain Ainsworth <zerooa@googlemail.com> for coming up
with the idea for this patch and hashing out the implementation
with me on irc.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_drv.h        |    6 ++++++
 drivers/gpu/drm/i915/i915_gem.c        |    9 +++++++++
 drivers/gpu/drm/i915/i915_gem_tiling.c |   26 ++++++--------------------
 3 files changed, 21 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 7aec3ec..174269c 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -698,6 +698,12 @@ struct drm_i915_gem_object {
 	 */
 	int fence_reg;
 
+	/**
+	 * Tiling changes can happen asynchronous to avoid gpu stalls.
+	 * This will be set if the current fencing may be invalid.
+	 */
+	int fence_invalid;
+
 	/** How many users have pinned this object in GTT space */
 	int pin_count;
 
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 8e73a12..8e18c9d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2485,6 +2485,8 @@ i915_gem_object_get_fence_reg(struct drm_gem_object *obj)
 	struct drm_i915_fence_reg *reg = NULL;
 	int ret;
 
+	BUG_ON(obj_priv->fence_invalid);
+
 	/* Just update our place in the LRU if our fence is getting used. */
 	if (obj_priv->fence_reg != I915_FENCE_REG_NONE) {
 		list_move_tail(&obj_priv->fence_list, &dev_priv->mm.fence_list);
@@ -2554,6 +2556,13 @@ i915_gem_object_adjust_fencing(struct drm_gem_object *obj)
 	struct drm_i915_gem_object *obj_priv = to_intel_bo(obj);
 	int ret;
 
+	if (obj_priv->fence_invalid) {
+		ret = i915_gem_object_put_fence_reg(obj);
+		if (ret != 0)
+			return ret;
+	}
+	obj_priv->fence_invalid = 0;
+
 	if (!i915_gem_object_fence_offset_ok(obj, obj_priv->tiling_mode)) {
 		ret = i915_gem_object_unbind(obj);
 		if (ret != 0)
diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
index 00f264d..aadaaa6 100644
--- a/drivers/gpu/drm/i915/i915_gem_tiling.c
+++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
@@ -322,30 +322,16 @@ i915_gem_set_tiling(struct drm_device *dev, void *data,
 	mutex_lock(&dev->struct_mutex);
 	if (args->tiling_mode != obj_priv->tiling_mode ||
 	    args->stride != obj_priv->stride) {
-		/* We need to rebind the object if its current allocation
-		 * no longer meets the alignment restrictions for its new
-		 * tiling mode. Otherwise we can just leave it alone, but
-		 * need to ensure that any fence register is cleared.
-		 */
-		if (!i915_gem_object_fence_offset_ok(obj, args->tiling_mode))
-			ret = i915_gem_object_unbind(obj);
-		else if (obj_priv->fence_reg != I915_FENCE_REG_NONE)
-			ret = i915_gem_object_put_fence_reg(obj);
-		else
-			i915_gem_release_mmap(obj);
-
-		if (ret != 0) {
-			WARN(ret != -ERESTARTSYS,
-			     "failed to reset object for tiling switch");
-			args->tiling_mode = obj_priv->tiling_mode;
-			args->stride = obj_priv->stride;
-			goto err;
-		}
+		/* Change tiling parameter asynchronously to avoid
+		 * gpu stalls. */
+		obj_priv->fence_invalid = 1;
+
+		i915_gem_release_mmap(obj);
 
 		obj_priv->tiling_mode = args->tiling_mode;
 		obj_priv->stride = args->stride;
 	}
-err:
+
 	drm_gem_object_unreference(obj);
 	mutex_unlock(&dev->struct_mutex);
 
-- 
1.6.6.1