Re: [PATCH v2 2/5] drm/i915: Do not make assumptions on GGTT VMA sizes

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On 04/30/2015 12:19 PM, Joonas Lahtinen wrote:

GGTT VMA sizes might be smaller than the whole object size due to
different GGTT views.

v2:
- Separate GGTT view constraint calculations from normal view
   constraint calculations (Chris Wilson)
v3:
- Do not bother with debug wording. (Tvrtko Ursulin)

Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
---
  drivers/gpu/drm/i915/i915_gem.c     | 103 +++++++++++++++++++++++-------------
  drivers/gpu/drm/i915/i915_gem_gtt.c |  23 ++++++++
  drivers/gpu/drm/i915/i915_gem_gtt.h |   4 ++
  3 files changed, 92 insertions(+), 38 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index e8f6f4c..9717c9d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3497,7 +3497,8 @@ static bool i915_gem_valid_gtt_space(struct i915_vma *vma,
  }

  /**
- * Finds free space in the GTT aperture and binds the object there.
+ * Finds free space in the GTT aperture and binds the object or a view of it
+ * there.
   */
  static struct i915_vma *
  i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj,
@@ -3516,36 +3517,60 @@ i915_gem_object_bind_to_vm(struct drm_i915_gem_object *obj,
  	struct i915_vma *vma;
  	int ret;

-	if(WARN_ON(i915_is_ggtt(vm) != !!ggtt_view))
-		return ERR_PTR(-EINVAL);
+	if (i915_is_ggtt(vm)) {
+		u32 view_size;
+
+		if (WARN_ON(!ggtt_view))
+			return ERR_PTR(-EINVAL);

-	fence_size = i915_gem_get_gtt_size(dev,
-					   obj->base.size,
-					   obj->tiling_mode);
-	fence_alignment = i915_gem_get_gtt_alignment(dev,
-						     obj->base.size,
-						     obj->tiling_mode, true);
-	unfenced_alignment =
-		i915_gem_get_gtt_alignment(dev,
-					   obj->base.size,
-					   obj->tiling_mode, false);
+		view_size = i915_ggtt_view_size(obj, ggtt_view);
+
+		fence_size = i915_gem_get_gtt_size(dev,
+						   view_size,
+						   obj->tiling_mode);
+		fence_alignment = i915_gem_get_gtt_alignment(dev,
+							     view_size,
+							     obj->tiling_mode,
+							     true);
+		unfenced_alignment = i915_gem_get_gtt_alignment(dev,
+								view_size,
+								obj->tiling_mode,
+								false);
+		size = flags & PIN_MAPPABLE ? fence_size : view_size;
+	} else {
+		fence_size = i915_gem_get_gtt_size(dev,
+						   obj->base.size,
+						   obj->tiling_mode);
+		fence_alignment = i915_gem_get_gtt_alignment(dev,
+							     obj->base.size,
+							     obj->tiling_mode,
+							     true);
+		unfenced_alignment =
+			i915_gem_get_gtt_alignment(dev,
+						   obj->base.size,
+						   obj->tiling_mode,
+						   false);
+		size = flags & PIN_MAPPABLE ? fence_size : obj->base.size;
+	}

I do not like this almost identical branches - so I defer to Chris to okay that this is what he wanted.

  	if (alignment == 0)
  		alignment = flags & PIN_MAPPABLE ? fence_alignment :
  						unfenced_alignment;
  	if (flags & PIN_MAPPABLE && alignment & (fence_alignment - 1)) {
-		DRM_DEBUG("Invalid object alignment requested %u\n", alignment);
+		DRM_DEBUG("Invalid object (view type=%u) alignment requested %u\n",
+			  ggtt_view ? ggtt_view->type : 0,
+			  alignment);
  		return ERR_PTR(-EINVAL);
  	}

-	size = flags & PIN_MAPPABLE ? fence_size : obj->base.size;
-
-	/* If the object is bigger than the entire aperture, reject it early
-	 * before evicting everything in a vain attempt to find space.
+	/* If binding the object/GGTT view requires more space than the entire
+	 * aperture has, reject it early before evicting everything in a vain
+	 * attempt to find space.
  	 */
-	if (obj->base.size > end) {
-		DRM_DEBUG("Attempting to bind an object larger than the aperture: object=%zd > %s aperture=%lu\n",
-			  obj->base.size,
+	if (size > end) {
+		DRM_DEBUG("Attempting to bind an object (view type=%u) larger than the aperture: size=%u > %s aperture=%lu\n",
+			  ggtt_view ? ggtt_view->type : 0,
+			  size,
  			  flags & PIN_MAPPABLE ? "mappable" : "total",
  			  end);
  		return ERR_PTR(-E2BIG);
@@ -4207,28 +4232,30 @@ i915_gem_object_do_pin(struct drm_i915_gem_object *obj,
  			return ret;
  	}

-	if ((bound ^ vma->bound) & GLOBAL_BIND) {
-		bool mappable, fenceable;
-		u32 fence_size, fence_alignment;
+	if (!ggtt_view || ggtt_view->type == I915_GGTT_VIEW_NORMAL) {
+		if ((bound ^ vma->bound) & GLOBAL_BIND) {

I still don't get this. !ggtt_view means GLOBAL_BIND cannot be set, what am I missing? It wouldn't work if the condition was just the type check?

+			bool mappable, fenceable;
+			u32 fence_size, fence_alignment;

-		fence_size = i915_gem_get_gtt_size(obj->base.dev,
-						   obj->base.size,
-						   obj->tiling_mode);
-		fence_alignment = i915_gem_get_gtt_alignment(obj->base.dev,
-							     obj->base.size,
-							     obj->tiling_mode,
-							     true);
+			fence_size = i915_gem_get_gtt_size(obj->base.dev,
+							   obj->base.size,
+							   obj->tiling_mode);
+			fence_alignment = i915_gem_get_gtt_alignment(obj->base.dev,
+								     obj->base.size,
+								     obj->tiling_mode,
+								     true);

-		fenceable = (vma->node.size == fence_size &&
-			     (vma->node.start & (fence_alignment - 1)) == 0);
+			fenceable = (vma->node.size == fence_size &&
+				     (vma->node.start & (fence_alignment - 1)) == 0);

-		mappable = (vma->node.start + fence_size <=
-			    dev_priv->gtt.mappable_end);
+			mappable = (vma->node.start + fence_size <=
+				    dev_priv->gtt.mappable_end);

-		obj->map_and_fenceable = mappable && fenceable;
-	}
+			obj->map_and_fenceable = mappable && fenceable;
+		}

-	WARN_ON(flags & PIN_MAPPABLE && !obj->map_and_fenceable);
+		WARN_ON(flags & PIN_MAPPABLE && !obj->map_and_fenceable);
+	}

  	vma->pin_count++;
  	return 0;
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index fc562c6..640584f 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -2847,3 +2847,26 @@ int i915_vma_bind(struct i915_vma *vma, enum i915_cache_level cache_level,

  	return 0;
  }
+
+/**
+ * i915_ggtt_view_size - Get the size of a GGTT view.
+ * @obj: Object the view is of.
+ * @view: The view in question.
+ *
+ * @return The size of the GGTT view in bytes.
+ */
+size_t
+i915_ggtt_view_size(struct drm_i915_gem_object *obj,
+		    const struct i915_ggtt_view *view)
+{
+	BUG_ON(!view);

It is a marginal point, but I wonder is size zero could be considered as a failure value and acted upon from the caller more gracefuly.

And in general I wonder if something like I915_BUG_ON which would re-route fops to fail-all and grab struct_mutex, or something, would maybe be an option.

Regards,

Tvrtko
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