reservation: update api and add some helpers

Move the list of shared fences to a struct, and return it in
reservation_object_get_list().
Add reservation_object_get_excl to get the exclusive fence.

Add reservation_object_reserve_shared(), which reserves space
in the reservation_object for 1 more shared fence.

reservation_object_add_shared_fence() and
reservation_object_add_excl_fence() are used to assign a new
fence to a reservation_object pointer, to complete a reservation.

Changes since v1:
- Add reservation_object_get_excl, reorder code a bit.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/dma-buf/reservation.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2012-2013 Canonical Ltd
+ * Copyright (C) 2012-2014 Canonical Ltd (Maarten Lankhorst)
  *
  * Based on bo.c which bears the following copyright notice,
  * but is dual licensed:
@@ -37,3 +37,157 @@
 
 DEFINE_WW_CLASS(reservation_ww_class);
 EXPORT_SYMBOL(reservation_ww_class);
+
+/*
+ * Reserve space to add a shared fence to a reservation_object,
+ * must be called with obj->lock held.
+ */
+int reservation_object_reserve_shared(struct reservation_object *obj)
+{
+	struct reservation_object_list *fobj, *old;
+	u32 max;
+
+	old = reservation_object_get_list(obj);
+
+	if (old && old->shared_max) {
+		if (old->shared_count < old->shared_max) {
+			/* perform an in-place update */
+			kfree(obj->staged);
+			obj->staged = NULL;
+			return 0;
+		} else
+			max = old->shared_max * 2;
+	} else
+		max = 4;
+
+	/*
+	 * resize obj->staged or allocate if it doesn't exist,
+	 * noop if already correct size
+	 */
+	fobj = krealloc(obj->staged, offsetof(typeof(*fobj), shared[max]),
+			GFP_KERNEL);
+	if (!fobj)
+		return -ENOMEM;
+
+	obj->staged = fobj;
+	fobj->shared_max = max;
+	return 0;
+}
+EXPORT_SYMBOL(reservation_object_reserve_shared);
+
+static void
+reservation_object_add_shared_inplace(struct reservation_object *obj,
+				      struct reservation_object_list *fobj,
+				      struct fence *fence)
+{
+	u32 i;
+
+	for (i = 0; i < fobj->shared_count; ++i) {
+		if (fobj->shared[i]->context == fence->context) {
+			struct fence *old_fence = fobj->shared[i];
+
+			fence_get(fence);
+
+			fobj->shared[i] = fence;
+
+			fence_put(old_fence);
+			return;
+		}
+	}
+
+	fence_get(fence);
+	fobj->shared[fobj->shared_count] = fence;
+	/*
+	 * make the new fence visible before incrementing
+	 * fobj->shared_count
+	 */
+	smp_wmb();
+	fobj->shared_count++;
+}
+
+static void
+reservation_object_add_shared_replace(struct reservation_object *obj,
+				      struct reservation_object_list *old,
+				      struct reservation_object_list *fobj,
+				      struct fence *fence)
+{
+	unsigned i;
+
+	fence_get(fence);
+
+	if (!old) {
+		fobj->shared[0] = fence;
+		fobj->shared_count = 1;
+		goto done;
+	}
+
+	/*
+	 * no need to bump fence refcounts, rcu_read access
+	 * requires the use of kref_get_unless_zero, and the
+	 * references from the old struct are carried over to
+	 * the new.
+	 */
+	fobj->shared_count = old->shared_count;
+
+	for (i = 0; i < old->shared_count; ++i) {
+		if (fence && old->shared[i]->context == fence->context) {
+			fence_put(old->shared[i]);
+			fobj->shared[i] = fence;
+			fence = NULL;
+		} else
+			fobj->shared[i] = old->shared[i];
+	}
+	if (fence)
+		fobj->shared[fobj->shared_count++] = fence;
+
+done:
+	obj->fence = fobj;
+	kfree(old);
+}
+
+/*
+ * Add a fence to a shared slot, obj->lock must be held, and
+ * reservation_object_reserve_shared_fence has been called.
+ */
+void reservation_object_add_shared_fence(struct reservation_object *obj,
+					 struct fence *fence)
+{
+	struct reservation_object_list *old, *fobj = obj->staged;
+
+	old = reservation_object_get_list(obj);
+	obj->staged = NULL;
+
+	if (!fobj) {
+		BUG_ON(old->shared_count == old->shared_max);
+		reservation_object_add_shared_inplace(obj, old, fence);
+	} else
+		reservation_object_add_shared_replace(obj, old, fobj, fence);
+}
+EXPORT_SYMBOL(reservation_object_add_shared_fence);
+
+void reservation_object_add_excl_fence(struct reservation_object *obj,
+				       struct fence *fence)
+{
+	struct fence *old_fence = obj->fence_excl;
+	struct reservation_object_list *old;
+	u32 i = 0;
+
+	old = reservation_object_get_list(obj);
+	if (old) {
+		i = old->shared_count;
+		old->shared_count = 0;
+	}
+
+	if (fence)
+		fence_get(fence);
+
+	obj->fence_excl = fence;
+
+	/* inplace update, no shared fences */
+	while (i--)
+		fence_put(old->shared[i]);
+
+	if (old_fence)
+		fence_put(old_fence);
+}
+EXPORT_SYMBOL(reservation_object_add_excl_fence);