From: Christoph Hellwig <email@example.com> To: Russell King - ARM Linux admin <firstname.lastname@example.org> Cc: Christoph Hellwig <email@example.com>, firstname.lastname@example.org, Robin Murphy <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [PATCH 1/4] vmalloc: lift the arm flag for coherent mappings to common code Date: Fri, 30 Aug 2019 16:59:35 +0200 [thread overview] Message-ID: <20190830145935.GA19838@lst.de> (raw) In-Reply-To: <20190830092918.GV13294@shell.armlinux.org.uk> On Fri, Aug 30, 2019 at 10:29:18AM +0100, Russell King - ARM Linux admin wrote: > On Fri, Aug 30, 2019 at 08:29:21AM +0200, Christoph Hellwig wrote: > > The arm architecture had a VM_ARM_DMA_CONSISTENT flag to mark DMA > > coherent remapping for a while. Lift this flag to common code so > > that we can use it generically. We also check it in the only place > > VM_USERMAP is directly check so that we can entirely replace that > > flag as well (although I'm not even sure why we'd want to allow > > remapping DMA appings, but I'd rather not change behavior). > > Good, because if you did change that behaviour, you'd break almost > every ARM framebuffer and cripple ARM audio drivers. How would that break them? All the usual video and audio drivers that use dma_alloc_* then use dma_mmap_* which never end up in the only place that actually checks VM_USERMAP (remap_vmalloc_range_partial) as they end up in the dma_map_ops mmap methods which contain what is effecitvely open coded versions of that routine. There are very few callers of remap_vmalloc_range_partial / remap_vmalloc_range, and while a few of those actually are in media drivers and the virtual frame buffer video driver, none of these seems to be called on dma memory (which would be a layering violation anyway).
next prev parent reply other threads:[~2019-08-30 14:59 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-08-30 6:29 cleanup vmap usage in the dma-mapping layer Christoph Hellwig 2019-08-30 6:29 ` [PATCH 1/4] vmalloc: lift the arm flag for coherent mappings to common code Christoph Hellwig 2019-08-30 9:29 ` Russell King - ARM Linux admin 2019-08-30 14:59 ` Christoph Hellwig [this message] 2019-08-30 6:29 ` [PATCH 2/4] dma-mapping: always use VM_DMA_COHERENT for generic DMA remap Christoph Hellwig 2019-08-30 6:29 ` [PATCH 3/4] dma-mapping: introduce a dma_common_find_pages helper Christoph Hellwig 2019-10-02 12:05 ` Geert Uytterhoeven 2019-10-02 16:45 ` Robin Murphy 2019-10-06 18:45 ` Christoph Hellwig 2019-10-07 7:35 ` Geert Uytterhoeven 2019-08-30 6:29 ` [PATCH 4/4] arm: remove wrappers for the generic dma remap helpers Christoph Hellwig
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