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Date: Tue, 30 Apr 2019 17:18:33 +0200 From: Christoph Hellwig <hch@....de> To: Robin Murphy <robin.murphy@....com> Cc: Christoph Hellwig <hch@....de>, Nicolin Chen <nicoleotsuka@...il.com>, m.szyprowski@...sung.com, vdumpa@...dia.com, linux@...linux.org.uk, catalin.marinas@....com, will.deacon@....com, chris@...kel.net, jcmvbkbc@...il.com, joro@...tes.org, dwmw2@...radead.org, tony@...mide.com, akpm@...ux-foundation.org, sfr@...b.auug.org.au, treding@...dia.com, keescook@...omium.org, iamjoonsoo.kim@....com, wsa+renesas@...g-engineering.com, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-xtensa@...ux-xtensa.org, iommu@...ts.linux-foundation.org Subject: Re: [RFC/RFT PATCH 1/2] dma-contiguous: Simplify dma_*_from_contiguous() function calls On Tue, Apr 30, 2019 at 01:37:54PM +0100, Robin Murphy wrote: > On 30/04/2019 11:56, Christoph Hellwig wrote: >> So while I really, really like this cleanup it turns out it isn't >> actually safe for arm :( arm remaps the CMA allocation in place >> instead of using a new mapping, which can be done because they don't >> share PMDs with the kernel. >> >> So we'll probably need a __dma_alloc_from_contiguous version with >> an additional bool fallback argument - everyone but arms uses >> dma_alloc_from_contiguous as in your patch, just arm will get the >> non-fallback one. > > Or we even just implement dma_{alloc,free}_contiguous() as a wrapper around > the existing APIs so that users can be thoroughly checked and converted > one-by-one. Yeah. Actually given all the contention I wonder if the easiest solution for now is to just open code the cma_alloc/cma_free calls in dma-direct and dma-iommu, with the hopes that everyone is going to migrate to those implementations in the mid-term anyway and dma_alloc_from_contiguous / dma_release_from_contiguous just go away..
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