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From:   dillon min <dillon.minfei@gmail.com>
Date:   Wed, 10 Jun 2020 10:24:10 +0800
Message-ID: <CAL9mu0KejK9JRrJg5tFb5xKGjaEYr=XRpvGB2nuBfnhLeBMdng@mail.gmail.com>
Subject: Re: [PATCH 2/2] arm-nommu: Add use_reserved_mem() to check if device
 support reserved memory
To:     Christoph Hellwig <hch@lst.de>
Cc:     Vladimir Murzin <vladimir.murzin@arm.com>,
        Rob Herring <robh+dt@kernel.org>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        linux@armlinux.org.uk, Kate Stewart <kstewart@linuxfoundation.org>,
        allison@lohutok.net, info@metux.net, tglx@linutronix.de,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        linux-stm32@st-md-mailman.stormreply.com,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Vladimir,

I tested your changes, it's working fine on stm32f429-disco(armv7m,
without cache) board.
you can submit a separate patch for dma-direct support on non-mmu
platform, i will drop mine.

thanks.

best regards.

Dillon,
On Wed, Jun 10, 2020 at 1:34 AM Christoph Hellwig <hch@lst.de> wrote:
>
> 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.

Yes, thanks Christoph's input.