linux-kernel - Re: clean up and modularize arch dma

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Date:   Sat, 24 Jun 2017 09:18:55 +0200
From:   Christoph Hellwig <hch@....de>
To:     tndave <tushar.n.dave@...cle.com>
Cc:     Christoph Hellwig <hch@....de>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        xen-devel@...ts.xenproject.org, linux-c6x-dev@...ux-c6x.org,
        linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-mips@...ux-mips.org, openrisc@...ts.librecores.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, dmaengine@...r.kernel.org,
        linux-tegra@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-samsung-soc@...r.kernel.org,
        iommu@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: clean up and modularize arch dma_mapping interface V2

On Wed, Jun 21, 2017 at 12:24:28PM -0700, tndave wrote:
> Thanks for doing this.
> So archs can still have their own definition for dma_set_mask() if 
> HAVE_ARCH_DMA_SET_MASK is y?
> (and similarly for dma_set_coherent_mask() when 
> CONFIG_ARCH_HAS_DMA_SET_COHERENT_MASK is y)
> Any plan to change these?

Yes, those should go away, but I'm not entirely sure how yet.  We'll
need some hook for switching between an IOMMU and a direct mapping
(I guess that's what you want to do for sparc as well?), and I need
to find the best way to do that.  Reimplementing all of dma_set_mask
and dma_set_coherent_mask is something that I want to move away from.