drm: rcar-du: Do not assume VSP has IOMMU

While running under Xen all the IOMMUs belong to
the hypervisor, thus the assumption that VSP is backed
by the IOMMU is wrong. Use CMA helper for this use-case then.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>

drivers/gpu/drm/rcar-du/rcar_du_kms.c

@@ -184,6 +184,14 @@ struct drm_gem_object *rcar_du_gem_prime_import_sg_table(struct drm_device *dev,
 				struct dma_buf_attachment *attach,
 				struct sg_table *sgt)
 {
+#ifdef CONFIG_XEN
+	/*
+	 * While running under Xen all the IOMMUs belong to
+	 * the hypervisor, thus the assumption that VSP is backed
+	 * by the IOMMU is wrong. Use CMA helper for this use-case then.
+	 */
+	return drm_gem_cma_prime_import_sg_table(dev, attach, sgt);
+#else
 	struct rcar_du_device *rcdu = dev->dev_private;
 	struct drm_gem_cma_object *cma_obj;
 	struct drm_gem_object *gem_obj;
@@ -216,6 +224,7 @@ struct drm_gem_object *rcar_du_gem_prime_import_sg_table(struct drm_device *dev,
 error:
 	kfree(cma_obj);
 	return ERR_PTR(ret);
+#endif
 }
 
 int rcar_du_dumb_create(struct drm_file *file, struct drm_device *dev,