drm/nouveau: embed gem object in nouveau_bo

There is no reason to keep the gem object separately allocated. nouveau is
the last user of gem_obj->driver_private, so if we embed it, we can get
rid of 8bytes per gem-object.

The implementation follows the radeon driver. bo->gem is only valid, iff
the bo was created via the gem helpers _and_ iff the user holds a valid
gem reference. That is, as the gem object holds a reference to the
nouveau_bo. If you use nouveau_ref() to gain a bo reference, you are not
guaranteed to also hold a gem reference. The gem object might get
destroyed after the last user drops the gem-ref via
drm_gem_object_unreference(). Use drm_gem_object_reference() to gain a
gem-reference.

For debugging, we can use bo->gem.filp != NULL to test whether a gem-bo is
valid. However, this shouldn't be used for real functionality to avoid
gem-internal dependencies.

Note that the implementation follows the previous style. However, we no
longer can check for bo->gem != NULL to test for a valid gem object. This
wasn't done before, so we should be safe now.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/drivers/gpu/drm/nouveau/nouveau_prime.c b/drivers/gpu/drm/nouveau/nouveau_prime.c
index e90468d5e5c0..51a2cb102b44 100644
--- a/drivers/gpu/drm/nouveau/nouveau_prime.c
+++ b/drivers/gpu/drm/nouveau/nouveau_prime.c
@@ -71,14 +71,16 @@ struct drm_gem_object *nouveau_gem_prime_import_sg_table(struct drm_device *dev,
 		return ERR_PTR(ret);
 
 	nvbo->valid_domains = NOUVEAU_GEM_DOMAIN_GART;
-	nvbo->gem = drm_gem_object_alloc(dev, nvbo->bo.mem.size);
-	if (!nvbo->gem) {
+
+	/* Initialize the embedded gem-object. We return a single gem-reference
+	 * to the caller, instead of a normal nouveau_bo ttm reference. */
+	ret = drm_gem_object_init(dev, &nvbo->gem, nvbo->bo.mem.size);
+	if (ret) {
 		nouveau_bo_ref(NULL, &nvbo);
 		return ERR_PTR(-ENOMEM);
 	}
 
-	nvbo->gem->driver_private = nvbo;
-	return nvbo->gem;
+	return &nvbo->gem;
 }
 
 int nouveau_gem_prime_pin(struct drm_gem_object *obj)