drm/i915: Reorganise rules for get_fence/put_fence

By simplifying the rules to calling get_fence when writing to the
through the GTT in a tiled manner, and calling put_fence before writing
to the object through the GTT in a linear manner, the code becomes
clearer and there is less chance of making a mistake.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
[danvet: fixed up conflict with ppgtt code and spelling in a new
comment.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1256,13 +1256,15 @@ int __must_check i915_gem_object_get_fence(struct drm_i915_gem_object *obj,
 					   struct intel_ring_buffer *pipelined);
 int __must_check i915_gem_object_put_fence(struct drm_i915_gem_object *obj);
 
-static inline void
+static inline bool
 i915_gem_object_pin_fence(struct drm_i915_gem_object *obj)
 {
 	if (obj->fence_reg != I915_FENCE_REG_NONE) {
 		struct drm_i915_private *dev_priv = obj->base.dev->dev_private;
 		dev_priv->fence_regs[obj->fence_reg].pin_count++;
-	}
+		return true;
+	} else
+		return false;
 }
 
 static inline void

drivers/gpu/drm/i915/i915_gem.c

@@ -1078,9 +1078,6 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	if (!obj->has_global_gtt_mapping)
 		i915_gem_gtt_bind_object(obj, obj->cache_level);
 
-	if (obj->tiling_mode == I915_TILING_NONE)
-		ret = i915_gem_object_put_fence(obj);
-	else
 	ret = i915_gem_object_get_fence(obj, NULL);
 	if (ret)
 		goto unlock;
@@ -2395,19 +2392,19 @@ i915_find_fence_reg(struct drm_device *dev,
 }
 
 /**
- * i915_gem_object_get_fence - set up a fence reg for an object
+ * i915_gem_object_get_fence - set up fencing for an object
  * @obj: object to map through a fence reg
  * @pipelined: ring on which to queue the change, or NULL for CPU access
- * @interruptible: must we wait uninterruptibly for the register to retire?
  *
  * When mapping objects through the GTT, userspace wants to be able to write
  * to them without having to worry about swizzling if the object is tiled.
- *
  * This function walks the fence regs looking for a free one for @obj,
  * stealing one if it can't find any.
  *
  * It then sets up the reg based on the object's properties: address, pitch
  * and tiling format.
+ *
+ * For an untiled surface, this removes any existing fence.
  */
 int
 i915_gem_object_get_fence(struct drm_i915_gem_object *obj,
@@ -2418,6 +2415,9 @@ i915_gem_object_get_fence(struct drm_i915_gem_object *obj,
 	struct drm_i915_fence_reg *reg;
 	int ret;
 
+	if (obj->tiling_mode == I915_TILING_NONE)
+		return i915_gem_object_put_fence(obj);
+
 	/* XXX disable pipelining. There are bugs. Shocking. */
 	pipelined = NULL;
 

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -530,18 +530,13 @@ pin_and_fence_object(struct drm_i915_gem_object *obj,
 
 	if (has_fenced_gpu_access) {
 		if (entry->flags & EXEC_OBJECT_NEEDS_FENCE) {
-			if (obj->tiling_mode) {
 			ret = i915_gem_object_get_fence(obj, ring);
 			if (ret)
 				goto err_unpin;
 
+			if (i915_gem_object_pin_fence(obj))
 				entry->flags |= __EXEC_OBJECT_HAS_FENCE;
-				i915_gem_object_pin_fence(obj);
-			} else {
-				ret = i915_gem_object_put_fence(obj);
-				if (ret)
-					goto err_unpin;
-			}
+
 			obj->pending_fenced_gpu_access = true;
 		}
 	}

drivers/gpu/drm/i915/intel_display.c

@@ -2152,13 +2152,11 @@ intel_pin_and_fence_fb_obj(struct drm_device *dev,
 	 * framebuffer compression.  For simplicity, we always install
 	 * a fence as the cost is not that onerous.
 	 */
-	if (obj->tiling_mode != I915_TILING_NONE) {
 	ret = i915_gem_object_get_fence(obj, pipelined);
 	if (ret)
 		goto err_unpin;
 
 	i915_gem_object_pin_fence(obj);
-	}
 
 	dev_priv->mm.interruptible = true;
 	return 0;