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Date:   Tue, 9 Jun 2020 19:34:55 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Vladimir Murzin <vladimir.murzin@arm.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        dillon min <dillon.minfei@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
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        linux@armlinux.org.uk, Kate Stewart <kstewart@linuxfoundation.org>,
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        <devicetree@vger.kernel.org>,
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        Linux ARM <linux-arm-kernel@lists.infradead.org>,
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Subject: Re: [PATCH 2/2] arm-nommu: Add use_reserved_mem() to check if
 device support reserved memory
Message-ID: <20200609173455.GA25467@lst.de>
References: <1591605038-8682-1-git-send-email-dillon.minfei@gmail.com> <1591605038-8682-3-git-send-email-dillon.minfei@gmail.com> <90df5646-e0c4-fcac-d934-4cc922230dd2@arm.com> <CAL9mu0+__0Z3R3TcSrj9-kPxsyQHKS9WqK1u58P0dEZ+Jd-wbQ@mail.gmail.com> <20200609153646.GA17969@lst.de> <031034fb-b109-7410-3ff8-e78cd12a5552@arm.com> <b0c85637-4646-614b-d406-49aa72ce52e1@arm.com>
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On Tue, Jun 09, 2020 at 05:25:04PM +0100, Vladimir Murzin wrote:
> Even though commit mentions ARM, I do not see how mmap would continue
> to work for NOMMU with dma-direct. ARM NOMMU needs it's own DMA operations
> only in cases where caches are implemented or active, in other cases it
> fully relies on dma-direct.

> It looks to me that we either should provide NOMMU variant for mmap in
> dma/direct or (carefully) fix dma/mapping.

I think dma-direct is the right place, the common helpers in
dma/mapping.c are basically the red headed stepchilds for misc
IOMMU drivers not covered by dma-iommu only.