Linux Virtualization - Apr 2019 - [RFC PATCH 03/12] s390/mm: force swiotlb for protected virtualization

> +++ b/arch/s390/include/asm/dma-mapping.h
> @@ -0,0 +1,13 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_S390_DMA_MAPPING_H
> +#define _ASM_S390_DMA_MAPPING_H
> +
> +#include <linux/dma-contiguous.h>
> +
> +static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type
*bus)
> +{
> +	return NULL;
> +}
> +
> +#endif /* _ASM_S390_DMA_MAPPING_H */
> +
Congratulations!  You ust create an entirely pointless duplicate of
include/asm-generic/dma-mapping.h.