linux-kernel - remove default fallbacks in dma_map

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Date:   Thu, 25 Jul 2019 08:33:56 +0200
From:   Christoph Hellwig <hch@....de>
To:     iommu@...ts.linux-foundation.org,
        Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Takashi Iwai <tiwai@...e.de>, Robin Murphy <robin.murphy@....com>,
        Michal Simek <monstr@...str.eu>,
        linux-arm-kernel@...ts.infradead.org,
        linux-m68k@...ts.linux-m68k.org, linux-parisc@...r.kernel.org,
        linux-sh@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: remove default fallbacks in dma_map_ops

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.