dma_common_mmap() and dma_common_get_sgtable() are defined in
drivers/base/dma-mapping.c, and always compiled if CONFIG_HAS_DMA=y.
However, their forward declarations and the inline functions defined on top
of them (dma_mmap_attrs(), dma_mmap_coherent(), dma_mmap_writecombine(),
dma_get_sgtable_attrs()), dma_get_sgtable()) are in
<asm-generic/dma-mapping-common.h>, which is not included by all
architectures supporting CONFIG_HAS_DMA=y. There exist no alternative
implementations.
Hence for e.g. m68k allmodconfig, I get:
drivers/media/v4l2-core/videobuf2-dma-contig.c: In function âvb2_dc_mmapâ:
drivers/media/v4l2-core/videobuf2-dma-contig.c:204: error: implicit declaration of function âdma_mmap_coherentâ
drivers/media/v4l2-core/videobuf2-dma-contig.c: In function âvb2_dc_get_base_sgtâ:
drivers/media/v4l2-core/videobuf2-dma-contig.c:387: error: implicit declaration of function âdma_get_sgtableâ
To fix this
- Move the forward declarations and inline definitions to
<linux/dma-mapping.h>, so all CONFIG_HAS_DMA=y architectures can use
them,
- Replace the hard "BUG_ON(!ops)" checks for dma_map_ops by soft checks,
so architectures can fall back to the common code by returning NULL
from their get_dma_ops(). Note that there are no "BUG_ON(!ops)" checks
in other functions in <asm-generic/dma-mapping-common.h>,
- Make "struct dma_map_ops *ops" const while we're at it.