linux-kernel - Re: [PATCH 07/11] powerpc: make dma_cache

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Message-ID: <20171003114330.GA24592@lst.de>
Date:   Tue, 3 Oct 2017 13:43:30 +0200
From:   Christoph Hellwig <hch@....de>
To:     Christophe LEROY <christophe.leroy@....fr>
Cc:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org,
        Chris Zankel <chris@...kel.net>,
        Michal Simek <monstr@...str.eu>, linux-ia64@...r.kernel.org,
        linux-mips@...ux-mips.org, linux-sh@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-xtensa@...ux-xtensa.org,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        David Howells <dhowells@...hat.com>,
        Max Filippov <jcmvbkbc@...il.com>,
        Guan Xuetao <gxt@...c.pku.edu.cn>,
        Robin Murphy <robin.murphy@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 07/11] powerpc: make dma_cache_sync a no-op

On Tue, Oct 03, 2017 at 01:24:57PM +0200, Christophe LEROY wrote:
>> powerpc does not implement DMA_ATTR_NON_CONSISTENT allocations, so it
>> doesn't make any sense to do any work in dma_cache_sync given that it
>> must be a no-op when dma_alloc_attrs returns coherent memory.
> What about arch/powerpc/mm/dma-noncoherent.c ?
>
> Powerpc 8xx doesn't have coherent memory.

It doesn't implement the DMA_ATTR_NON_CONSISTENT interface either,
so if it really doesn't have a way to provide dma coherent allocation
(although the code in __dma_alloc_coherent suggests it does provide
dma coherent allocations) I have no idea how it could ever have
worked.