drm/prime: Simplify drm_gem_remove_prime_handles

with the reworking semantics and locking of the obj->dma_buf pointer
this pointer is always set as long as there's still a gem handle
around and a dma_buf associated with this gem object.

Also, the per file-priv lookup-cache for dma-buf importing is also
unified between foreign and native objects.

Hence we don't need to special case the clean any more and can simply
drop the clause which only runs for foreing objects, i.e. with
obj->import_attach set.

Note that with this change (actually with the previous one to always
set up obj->dma_buf even for foreign objects) it is no longer required
to set obj->import_attach when importing a foreing object. So update
comments accordingly, too.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_gem.c

@@ -191,11 +191,6 @@ EXPORT_SYMBOL(drm_gem_object_alloc);
 static void
 drm_gem_remove_prime_handles(struct drm_gem_object *obj, struct drm_file *filp)
 {
-	if (obj->import_attach) {
-		drm_prime_remove_buf_handle(&filp->prime,
-				obj->import_attach->dmabuf);
-	}
-
 	/*
 	 * Note: obj->dma_buf can't disappear as long as we still hold a
 	 * handle reference in obj->handle_count.

include/drm/drmP.h

@@ -687,6 +687,11 @@ struct drm_gem_object {
 	 *
 	 * The driver's ->gem_free_object callback is responsible for cleaning
 	 * up the dma_buf attachment and references acquired at import time.
+	 *
+	 * Note that the drm gem/prime core does not depend upon drivers setting
+	 * this field any more. So for drivers where this doesn't make sense
+	 * (e.g. virtual devices or a displaylink behind an usb bus) they can
+	 * simply leave it as NULL.
 	 */
 	struct dma_buf_attachment *import_attach;
 };