Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 9 Jun 2020 17:36:46 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     dillon min <dillon.minfei@gmail.com>
Cc:     Vladimir Murzin <vladimir.murzin@arm.com>, hch@lst.de,
        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>
Subject: Re: [PATCH 2/2] arm-nommu: Add use_reserved_mem() to check if
 device support reserved memory
Message-ID: <20200609153646.GA17969@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>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAL9mu0+__0Z3R3TcSrj9-kPxsyQHKS9WqK1u58P0dEZ+Jd-wbQ@mail.gmail.com>
User-Agent: Mutt/1.5.17 (2007-11-01)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Jun 09, 2020 at 11:22:24PM +0800, dillon min wrote:
> Hi Vladimir,
> 
> Thanks for reviewing.
> 
> Hi Christoph Hellwig,
> 
> I just want to know if kernel dma mapping/direct is focused on
> platforms with MMU.
> leave arch code to handle dma coherent memory management themself for
> no-MMU platform.

No, I'd really like to consolidate everything that isn't overly
arch specific eventually.

> 
> so, you just return error code in kernel/dma/mapping.c,direct.c
> without CONFIG_MMU defined ?
> which means dma-direct mapping doesn't support !CONFIG_MMU is not a
> bug, but design as it's.
> or, just return error code currently, will add dma direct mapping
> support for !CONFIG_MMU in the
> future?
> 
> As Vladimir Murzin's suggestion has changes in kernel code, I need
> your input to get
> the design goal about dma-direct mapping, thanks.

Can someone repost the whole patch?