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Date:   Thu, 20 Aug 2020 06:52:01 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Tomasz Figa <tfiga@chromium.org>
Cc:     Robin Murphy <robin.murphy@arm.com>,
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Subject: Re: [PATCH 05/28] media/v4l2: remove
 V4L2-FLAG-MEMORY-NON-CONSISTENT
Message-ID: <20200820045201.GB4570@lst.de>
References: <20200819065555.1802761-1-hch@lst.de> <20200819065555.1802761-6-hch@lst.de> <CAAFQd5COLxjydDYrfx47ht8tj-aNPiaVnC+WyQA7nvpW4gs=ww@mail.gmail.com> <62e4f4fc-c8a5-3ee8-c576-fe7178cb4356@arm.com> <CAAFQd5AcCTDguB2C9KyDiutXWoEvBL8tL7+a==Uo8vj_8CLOJw@mail.gmail.com> <2b32f1d8-16f7-3352-40a5-420993d52fb5@arm.com> <CAAFQd5DrEq7UVi_aH=-DO4xYC3SbjJ3m1aQSbt=8THL-W+orMQ@mail.gmail.com>
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On Wed, Aug 19, 2020 at 04:22:29PM +0200, Tomasz Figa wrote:
> > > FWIW, I asked back in time what the plan is for non-coherent
> > > allocations and it seemed like DMA_ATTR_NON_CONSISTENT and
> > > dma_sync_*() was supposed to be the right thing to go with. [2] The
> > > same thread also explains why dma_alloc_pages() isn't suitable for the
> > > users of dma_alloc_attrs() and DMA_ATTR_NON_CONSISTENT.
> >
> > AFAICS even back then Christoph was implying getting rid of
> > NON_CONSISTENT and *replacing* it with something streaming-API-based -
> 
> That's not how I read his reply from the thread I pointed to, but that
> might of course be my misunderstanding.

Yes.  Without changes like in this series just calling dma_sync_single_*
will break in various cases, e.g. because dma_alloc_attrs returns
memory remapped in the vmalloc space, and the dma_sync_single_*
implementation implementation can't cope with vmalloc addresses.