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Date: Sat, 3 Aug 2019 12:30:24 +0200 From: Christoph Hellwig <hch@....de> To: Takashi Iwai <tiwai@...e.de> Cc: Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org, Marek Szyprowski <m.szyprowski@...sung.com>, linux-xtensa@...ux-xtensa.org, Michal Simek <monstr@...str.eu>, linux-parisc@...r.kernel.org, linux-sh@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, x86@...nel.org, linux-kernel@...r.kernel.org, linux-m68k@...ts.linux-m68k.org, Robin Murphy <robin.murphy@....com>, linux-arm-kernel@...ts.infradead.org Subject: Re: [PATCH 5/5] dma-mapping: remove ARCH_NO_COHERENT_DMA_MMAP On Fri, Aug 02, 2019 at 10:24:02AM +0200, Takashi Iwai wrote: > I wasn't careful enough to look at that change, sorry. > > The code there tries to check whether dma_mmap_coherent() would always > fail on some platforms. Then the driver clears the mmap capability > flag at the device open time and notifies user-space to fall back to > the dumb read/write mode. > > So I'm afraid that simply dropping the check would cause the behavior > regression, e.g. on PARISC. > > Is there any simple way to test whether dma_mmap_coherent() would work > or not in general on the target platform? It's not necessarily in an > ifdef at all. This isn't really a platform, but a per-device question. I can add a "bool dma_can_mmap(struct device *dev)" helper to check that. But how do I get at a suitable struct device in hw_support_mmap()?
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