linux-kernel - Re: [PATCH 2/5] dma-mapping: move the dma

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Date:   Tue, 11 Sep 2018 08:46:36 +0200
From:   Christoph Hellwig <hch@....de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Paul Burton <paul.burton@...s.com>, linux-mips@...ux-mips.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] dma-mapping: move the dma_coherent flag to struct
 device

On Mon, Sep 10, 2018 at 06:13:50PM +0200, Greg Kroah-Hartman wrote:
> > +#if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
> > +    defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) || \
> > +    defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
> > +	bool			dma_coherent:1;
> > +#endif
> 
> It's just one bit, why not always have it enabled here?  If the arch
> uses it or doesn't, no big deal.
> 
> Or are you using this to "catch" arches that mess something up?

Yes, that is the intent - I don't want architectures to accidentally
set it while not selecting the non-coherent infrastructure, as it
won't have an effect.