drm/i915: Refactor common list iteration over GGTT vma

In quite a few places, we have a list iteration over the vma on an
object that only want to inspect GGTT vma. By construction, these are
placed at the start of the list, so we have copied that knowledge into
many callsites. Pull that knowledge back to i915_vma.h and provide a
for_each_ggtt_vma() to tidy up the code.

v2: Add a backreference from vma_create() to remind ourselves why we put
ggtt vma at the head of the obj->vma_list (and ppgtt vma at the tail).
v3: Fixup s/vma/V/

Suggested-by: Joonas Lahtinen <[e-mail]>
Signed-off-by: Chris Wilson <[e-mail]>
Cc: Joonas Lahtinen <[e-mail]>
Reviewed-by: Daniel Vetter <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/i915/i915_debugfs.c

···
 	u64 size = 0;
 	struct i915_vma *vma;
 
-	list_for_each_entry(vma, &obj->vma_list, obj_link) {
-		if (i915_vma_is_ggtt(vma) && drm_mm_node_allocated(&vma->node))
+	for_each_ggtt_vma(vma, obj) {
+		if (drm_mm_node_allocated(&vma->node))
 			size += vma->node.size;
 	}
 

drivers/gpu/drm/i915/i915_gem.c

···
 		intel_fb_obj_flush(obj,
 				   fb_write_origin(obj, I915_GEM_DOMAIN_GTT));
 
-		list_for_each_entry(vma, &obj->vma_list, obj_link) {
-			if (!i915_vma_is_ggtt(vma))
-				break;
-
+		for_each_ggtt_vma(vma, obj) {
 			if (vma->iomap)
 				continue;
 
···
 
 	GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
 
-	list_for_each_entry(vma, &obj->vma_list, obj_link) {
-		if (!i915_vma_is_ggtt(vma))
-			break;
-
+	for_each_ggtt_vma(vma, obj) {
 		if (i915_vma_is_active(vma))
 			continue;
 
···
 	drm_vma_node_unmap(&obj->base.vma_node,
 			   obj->base.dev->anon_inode->i_mapping);
 
-	list_for_each_entry(vma, &obj->vma_list, obj_link) {
-		if (!i915_vma_is_ggtt(vma))
-			break;
-
+	for_each_ggtt_vma(vma, obj)
 		i915_vma_unset_userfault(vma);
-	}
 }
 
 /**
···
 			 * dropped the fence as all snoopable access is
 			 * supposed to be linear.
 			 */
-			list_for_each_entry(vma, &obj->vma_list, obj_link) {
+			for_each_ggtt_vma(vma, obj) {
 				ret = i915_vma_put_fence(vma);
 				if (ret)
 					return ret;

drivers/gpu/drm/i915/i915_gem_gtt.c

···
 		bool ggtt_bound = false;
 		struct i915_vma *vma;
 
-		list_for_each_entry(vma, &obj->vma_list, obj_link) {
-			if (vma->vm != &ggtt->base)
-				continue;
-
+		for_each_ggtt_vma(vma, obj) {
 			if (!i915_vma_unbind(vma))
 				continue;
 

drivers/gpu/drm/i915/i915_gem_tiling.c

···
 	if (tiling_mode == I915_TILING_NONE)
 		return 0;
 
-	list_for_each_entry(vma, &obj->vma_list, obj_link) {
-		if (!i915_vma_is_ggtt(vma))
-			break;
-
+	for_each_ggtt_vma(vma, obj) {
 		if (i915_vma_fence_prepare(vma, tiling_mode, stride))
 			continue;
 
···
 	}
 	mutex_unlock(&obj->mm.lock);
 
-	list_for_each_entry(vma, &obj->vma_list, obj_link) {
-		if (!i915_vma_is_ggtt(vma))
-			break;
-
+	for_each_ggtt_vma(vma, obj) {
 		vma->fence_size =
 			i915_gem_fence_size(i915, vma->size, tiling, stride);
 		vma->fence_alignment =

drivers/gpu/drm/i915/i915_vma.c

···
 								i915_gem_object_get_stride(obj));
 		GEM_BUG_ON(!is_power_of_2(vma->fence_alignment));
 
+		/*
+		 * We put the GGTT vma at the start of the vma-list, followed
+		 * by the ppGGTT vma. This allows us to break early when
+		 * iterating over only the GGTT vma for an object, see
+		 * for_each_ggtt_vma()
+		 */
 		vma->flags |= I915_VMA_GGTT;
 		list_add(&vma->obj_link, &obj->vma_list);
 	} else {

drivers/gpu/drm/i915/i915_vma.h

···
 		__i915_vma_unpin_fence(vma);
 }
 
-#endif
+#define for_each_until(cond) if (cond) break; else
 
+/**
+ * for_each_ggtt_vma - Iterate over the GGTT VMA belonging to an object.
+ * @V: the #i915_vma iterator
+ * @OBJ: the #drm_i915_gem_object
+ *
+ * GGTT VMA are placed at the being of the object's vma_list, see
+ * vma_create(), so we can stop our walk as soon as we see a ppgtt VMA,
+ * or the list is empty ofc.
+ */
+#define for_each_ggtt_vma(V, OBJ) \
+	list_for_each_entry(V, &(OBJ)->vma_list, obj_link)		\
+		for_each_until(!i915_vma_is_ggtt(V))
+
+#endif