# remove default fallbacks in dma\_map\_ops v3

- From: Christoph Hellwig \<hch@lst.de\>
- Date: 2019-08-08 16:00:35 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2019/08/5681963
- Thread: https://ratatoskr.run/linux-arm-kernel/2019/08/5681963/t.md

```text
Hi all,

we have a few places where the DMA mapping layer has non-trivial default
actions that are questionable and/or dangerous.

This series instead wires up the mmap, get_sgtable and get_required_mask
methods explicitly and cleans up some surrounding areas.  This also means
we could get rid of the ARCH_NO_COHERENT_DMA_MMAP kconfig option, as we
now require a mmap method wired up, or in case of non-coherent dma-direct
the presence of the arch_dma_coherent_to_pfn hook.  The only interesting
case is that the sound code also checked the ARCH_NO_COHERENT_DMA_MMAP
symbol in somewhat odd ways, so I'd like to see a review of the sound
situation before going forward with that patch.

Changes since v2:
 - fix use of dma_can_mmap in alsa
 - improve the CONFIG_* mess a little more

Changes since v1:
 - add a dma_can_mmap helper for alsa

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