drm/i915: Forgo last_fence active request tracking

We were using the last_fence to track the last request that used this
vma that might be interpreted by a fence register and forced ourselves
to wait for this request before modifying any fence register that
overlapped our vma. Due to requirement that we need to track any XY_BLT
command, linear or tiled, this in effect meant that we have to track the
vma for its active lifespan anyway, so we can forgo the explicit
last_fence tracking and just use the whole vma->active.

Another solution would be to pipeline the register updates, and would
help resolve some long running stalls for gen3 (but only gen 2 and 3!)
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190812174804.26180-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -212,9 +212,7 @@ describe_obj(struct seq_file *m, struct drm_i915_gem_object *obj)
 			}
 		}
 		if (vma->fence)
-			seq_printf(m, " , fence: %d%s",
-				   vma->fence->id,
-				   i915_active_request_isset(&vma->last_fence) ? "*" : "");
+			seq_printf(m, " , fence: %d", vma->fence->id);
 		seq_puts(m, ")");
 
 		spin_lock(&obj->vma.lock);

drivers/gpu/drm/i915/i915_gem_fence_reg.c

@@ -230,16 +230,14 @@ static int fence_update(struct i915_fence_reg *fence,
 			 i915_gem_object_get_tiling(vma->obj)))
 			return -EINVAL;
 
-		ret = i915_active_request_retire(&vma->last_fence,
-					     &vma->obj->base.dev->struct_mutex);
+		ret = i915_active_wait(&vma->active);
 		if (ret)
 			return ret;
 	}
 
 	old = xchg(&fence->vma, NULL);
 	if (old) {
-		ret = i915_active_request_retire(&old->last_fence,
-					     &old->obj->base.dev->struct_mutex);
+		ret = i915_active_wait(&old->active);
 		if (ret) {
 			fence->vma = old;
 			return ret;

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -1867,7 +1867,6 @@ static struct i915_vma *pd_vma_create(struct gen6_ppgtt *ppgtt, int size)
 		return ERR_PTR(-ENOMEM);
 
 	i915_active_init(i915, &vma->active, NULL, NULL);
-	INIT_ACTIVE_REQUEST(&vma->last_fence);
 
 	vma->vm = &ggtt->vm;
 	vma->ops = &pd_vma_ops;

drivers/gpu/drm/i915/i915_vma.c

@@ -120,7 +120,6 @@ vma_create(struct drm_i915_gem_object *obj,
 
 	i915_active_init(vm->i915, &vma->active,
 			 __i915_vma_active, __i915_vma_retire);
-	INIT_ACTIVE_REQUEST(&vma->last_fence);
 
 	/* Declare ourselves safe for use inside shrinkers */
 	if (IS_ENABLED(CONFIG_LOCKDEP)) {
@@ -802,8 +801,6 @@ static void __i915_vma_destroy(struct i915_vma *vma)
 	GEM_BUG_ON(vma->node.allocated);
 	GEM_BUG_ON(vma->fence);
 
-	GEM_BUG_ON(i915_active_request_isset(&vma->last_fence));
-
 	mutex_lock(&vma->vm->mutex);
 	list_del(&vma->vm_link);
 	mutex_unlock(&vma->vm->mutex);
@@ -928,9 +925,6 @@ int i915_vma_move_to_active(struct i915_vma *vma,
 	obj->read_domains |= I915_GEM_GPU_DOMAINS;
 	obj->mm.dirty = true;
 
-	if (flags & EXEC_OBJECT_NEEDS_FENCE)
-		__i915_active_request_set(&vma->last_fence, rq);
-
 	GEM_BUG_ON(!i915_vma_is_active(vma));
 	return 0;
 }
@@ -961,14 +955,7 @@ int i915_vma_unbind(struct i915_vma *vma)
 		 * before we are finished).
 		 */
 		__i915_vma_pin(vma);
-
 		ret = i915_active_wait(&vma->active);
-		if (ret)
-			goto unpin;
-
-		ret = i915_active_request_retire(&vma->last_fence,
-					      &vma->vm->i915->drm.struct_mutex);
-unpin:
 		__i915_vma_unpin(vma);
 		if (ret)
 			return ret;

drivers/gpu/drm/i915/i915_vma.h

@@ -111,7 +111,6 @@ struct i915_vma {
 #define I915_VMA_GGTT_WRITE	BIT(14)
 
 	struct i915_active active;
-	struct i915_active_request last_fence;
 
 	/**
 	 * Support different GGTT views into the same object.