On Linux `dma_length` field of `struct scatterlist` is present on the arches where DMA mapping code is able to coalesce adjacent segments of physical address space. It contains total length of coalesced segments while `length` field contains non-coalesced length of each segment. On other arches `dma_length` is aliased to `length` field with `sg_dma_len` macro. As FreeBSD does not merge scatterlist segments it do not have `dma_length` field. It is appered that at least i915kms driver depends on existence of `dma_length` field. Add the field and disable it by default. To enable add to Makefile .if ${MACHINE_CPUARCH} == "i386" || ${MACHINE_CPUARCH} == "amd64" || \\ ${MACHINE_CPUARCH} == "aarch64" || ${MACHINE_CPUARCH} == "powerpc" CFLAGS+= -DCONFIG_NEED_SG_DMA_LENGTH .endif Reported by: Ryan Fahy Reviewed by: bz MFC after: 1 month GHI: https://github.com/freebsd/drm-kmod/issues/315 Differential Revision: https://reviews.freebsd.org/D59630