drm/i915: Introduce drm_i915_gem_object_ops

In order to specialise functions depending upon the type of object, we
can attach vfuncs to each object via a new ->ops pointer.

For instance, this will be used in future patches to only bind pages from
a dma-buf for the duration that the object is used by the GPU - and so
prevent them from pinning those pages for the entire of the object.

v2: Bonus comments.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -899,9 +899,29 @@ enum i915_cache_level {
 	I915_CACHE_LLC_MLC, /* gen6+, in docs at least! */
 };
 
+struct drm_i915_gem_object_ops {
+	/* Interface between the GEM object and its backing storage.
+	 * get_pages() is called once prior to the use of the associated set
+	 * of pages before to binding them into the GTT, and put_pages() is
+	 * called after we no longer need them. As we expect there to be
+	 * associated cost with migrating pages between the backing storage
+	 * and making them available for the GPU (e.g. clflush), we may hold
+	 * onto the pages after they are no longer referenced by the GPU
+	 * in case they may be used again shortly (for example migrating the
+	 * pages to a different memory domain within the GTT). put_pages()
+	 * will therefore most likely be called when the object itself is
+	 * being released or under memory pressure (where we attempt to
+	 * reap pages for the shrinker).
+	 */
+	int (*get_pages)(struct drm_i915_gem_object *);
+	void (*put_pages)(struct drm_i915_gem_object *);
+};
+
 struct drm_i915_gem_object {
 	struct drm_gem_object base;
 
+	const struct drm_i915_gem_object_ops *ops;
+
 	/** Current space allocated to this object in the GTT, if any. */
 	struct drm_mm_node *gtt_space;
 	struct list_head gtt_list;
@@ -1306,7 +1326,8 @@ int i915_gem_wait_ioctl(struct drm_device *dev, void *data,
 			struct drm_file *file_priv);
 void i915_gem_load(struct drm_device *dev);
 int i915_gem_init_object(struct drm_gem_object *obj);
-void i915_gem_object_init(struct drm_i915_gem_object *obj);
+void i915_gem_object_init(struct drm_i915_gem_object *obj,
+			 const struct drm_i915_gem_object_ops *ops);
 struct drm_i915_gem_object *i915_gem_alloc_object(struct drm_device *dev,
 						  size_t size);
 void i915_gem_free_object(struct drm_gem_object *obj);
@@ -1319,7 +1340,7 @@ int __must_check i915_gem_object_unbind(struct drm_i915_gem_object *obj);
 void i915_gem_release_mmap(struct drm_i915_gem_object *obj);
 void i915_gem_lastclose(struct drm_device *dev);
 
-int __must_check i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj);
+int __must_check i915_gem_object_get_pages(struct drm_i915_gem_object *obj);
 int __must_check i915_mutex_lock_interruptible(struct drm_device *dev);
 int i915_gem_object_sync(struct drm_i915_gem_object *obj,
 			 struct intel_ring_buffer *to);

drivers/gpu/drm/i915/i915_gem.c

@@ -1650,18 +1650,12 @@ i915_gem_object_is_purgeable(struct drm_i915_gem_object *obj)
 	return obj->madv == I915_MADV_DONTNEED;
 }
 
-static int
+static void
 i915_gem_object_put_pages_gtt(struct drm_i915_gem_object *obj)
 {
 	int page_count = obj->base.size / PAGE_SIZE;
 	int ret, i;
 
-	BUG_ON(obj->gtt_space);
-
-	if (obj->pages == NULL)
-		return 0;
-
-	BUG_ON(obj->gtt_space);
 	BUG_ON(obj->madv == __I915_MADV_PURGED);
 
 	ret = i915_gem_object_set_to_cpu_domain(obj, true);
@@ -1693,9 +1687,21 @@ i915_gem_object_put_pages_gtt(struct drm_i915_gem_object *obj)
 
 	drm_free_large(obj->pages);
 	obj->pages = NULL;
+}
+
+static int
+i915_gem_object_put_pages(struct drm_i915_gem_object *obj)
+{
+	const struct drm_i915_gem_object_ops *ops = obj->ops;
+
+	if (obj->sg_table || obj->pages == NULL)
+		return 0;
+
+	BUG_ON(obj->gtt_space);
+
+	ops->put_pages(obj);
 
 	list_del(&obj->gtt_list);
-
 	if (i915_gem_object_is_purgeable(obj))
 		i915_gem_object_truncate(obj);
 
@@ -1712,7 +1718,7 @@ i915_gem_purge(struct drm_i915_private *dev_priv, long target)
 				 &dev_priv->mm.unbound_list,
 				 gtt_list) {
 		if (i915_gem_object_is_purgeable(obj) &&
-		    i915_gem_object_put_pages_gtt(obj) == 0) {
+		    i915_gem_object_put_pages(obj) == 0) {
 			count += obj->base.size >> PAGE_SHIFT;
 			if (count >= target)
 				return count;
@@ -1724,7 +1730,7 @@ i915_gem_purge(struct drm_i915_private *dev_priv, long target)
 				 mm_list) {
 		if (i915_gem_object_is_purgeable(obj) &&
 		    i915_gem_object_unbind(obj) == 0 &&
-		    i915_gem_object_put_pages_gtt(obj) == 0) {
+		    i915_gem_object_put_pages(obj) == 0) {
 			count += obj->base.size >> PAGE_SHIFT;
 			if (count >= target)
 				return count;
@@ -1742,10 +1748,10 @@ i915_gem_shrink_all(struct drm_i915_private *dev_priv)
 	i915_gem_evict_everything(dev_priv->dev);
 
 	list_for_each_entry_safe(obj, next, &dev_priv->mm.unbound_list, gtt_list)
-		i915_gem_object_put_pages_gtt(obj);
+		i915_gem_object_put_pages(obj);
 }
 
-int
+static int
 i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 {
 	struct drm_i915_private *dev_priv = obj->base.dev->dev_private;
@@ -1754,9 +1760,6 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 	struct page *page;
 	gfp_t gfp;
 
-	if (obj->pages || obj->sg_table)
-		return 0;
-
 	/* Assert that the object is not currently in any GPU domain. As it
 	 * wasn't in the GTT, there shouldn't be any way it could have been in
 	 * a GPU cache
@@ -1806,7 +1809,6 @@ i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 	if (i915_gem_object_needs_bit17_swizzle(obj))
 		i915_gem_object_do_bit_17_swizzle(obj);
 
-	list_add_tail(&obj->gtt_list, &dev_priv->mm.unbound_list);
 	return 0;
 
 err_pages:
@@ -1818,6 +1820,31 @@ err_pages:
 	return PTR_ERR(page);
 }
 
+/* Ensure that the associated pages are gathered from the backing storage
+ * and pinned into our object. i915_gem_object_get_pages() may be called
+ * multiple times before they are released by a single call to
+ * i915_gem_object_put_pages() - once the pages are no longer referenced
+ * either as a result of memory pressure (reaping pages under the shrinker)
+ * or as the object is itself released.
+ */
+int
+i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
+{
+	struct drm_i915_private *dev_priv = obj->base.dev->dev_private;
+	const struct drm_i915_gem_object_ops *ops = obj->ops;
+	int ret;
+
+	if (obj->sg_table || obj->pages)
+		return 0;
+
+	ret = ops->get_pages(obj);
+	if (ret)
+		return ret;
+
+	list_add_tail(&obj->gtt_list, &dev_priv->mm.unbound_list);
+	return 0;
+}
+
 void
 i915_gem_object_move_to_active(struct drm_i915_gem_object *obj,
 			       struct intel_ring_buffer *ring,
@@ -2071,7 +2098,6 @@ void i915_gem_reset(struct drm_device *dev)
 		obj->base.read_domains &= ~I915_GEM_GPU_DOMAINS;
 	}
 
-
 	/* The fence registers are invalidated so clear them out */
 	i915_gem_reset_fences(dev);
 }
@@ -2871,7 +2897,7 @@ i915_gem_object_bind_to_gtt(struct drm_i915_gem_object *obj,
 		return -E2BIG;
 	}
 
-	ret = i915_gem_object_get_pages_gtt(obj);
+	ret = i915_gem_object_get_pages(obj);
 	if (ret)
 		return ret;
 
@@ -3610,15 +3636,16 @@ unlock:
 	return ret;
 }
 
-void i915_gem_object_init(struct drm_i915_gem_object *obj)
+void i915_gem_object_init(struct drm_i915_gem_object *obj,
+			  const struct drm_i915_gem_object_ops *ops)
 {
-	obj->base.driver_private = NULL;
-
 	INIT_LIST_HEAD(&obj->mm_list);
 	INIT_LIST_HEAD(&obj->gtt_list);
 	INIT_LIST_HEAD(&obj->ring_list);
 	INIT_LIST_HEAD(&obj->exec_list);
 
+	obj->ops = ops;
+
 	obj->fence_reg = I915_FENCE_REG_NONE;
 	obj->madv = I915_MADV_WILLNEED;
 	/* Avoid an unnecessary call to unbind on the first bind. */
@@ -3627,6 +3654,11 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj)
 	i915_gem_info_add_obj(obj->base.dev->dev_private, obj->base.size);
 }
 
+static const struct drm_i915_gem_object_ops i915_gem_object_ops = {
+	.get_pages = i915_gem_object_get_pages_gtt,
+	.put_pages = i915_gem_object_put_pages_gtt,
+};
+
 struct drm_i915_gem_object *i915_gem_alloc_object(struct drm_device *dev,
 						  size_t size)
 {
@@ -3653,7 +3685,7 @@ struct drm_i915_gem_object *i915_gem_alloc_object(struct drm_device *dev,
 	mapping = obj->base.filp->f_path.dentry->d_inode->i_mapping;
 	mapping_set_gfp_mask(mapping, mask);
 
-	i915_gem_object_init(obj);
+	i915_gem_object_init(obj, &i915_gem_object_ops);
 
 	obj->base.write_domain = I915_GEM_DOMAIN_CPU;
 	obj->base.read_domains = I915_GEM_DOMAIN_CPU;
@@ -3711,7 +3743,7 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
 		dev_priv->mm.interruptible = was_interruptible;
 	}
 
-	i915_gem_object_put_pages_gtt(obj);
+	i915_gem_object_put_pages(obj);
 	i915_gem_object_free_mmap_offset(obj);
 
 	drm_gem_object_release(&obj->base);

drivers/gpu/drm/i915/i915_gem_dmabuf.c

@@ -41,7 +41,7 @@ static struct sg_table *i915_gem_map_dma_buf(struct dma_buf_attachment *attachme
 	if (ret)
 		return ERR_PTR(ret);
 
-	ret = i915_gem_object_get_pages_gtt(obj);
+	ret = i915_gem_object_get_pages(obj);
 	if (ret) {
 		sg = ERR_PTR(ret);
 		goto out;
@@ -89,7 +89,7 @@ static void *i915_gem_dmabuf_vmap(struct dma_buf *dma_buf)
 		goto out_unlock;
 	}
 
-	ret = i915_gem_object_get_pages_gtt(obj);
+	ret = i915_gem_object_get_pages(obj);
 	if (ret) {
 		mutex_unlock(&dev->struct_mutex);
 		return ERR_PTR(ret);