linux-kernel - Re: [PATCH 2/2] arm-nommu: Add use_reserved_mem() to check if device support reserved memory

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Message-ID: <20200609153646.GA17969@lst.de>
Date:   Tue, 9 Jun 2020 17:36:46 +0200
From:   Christoph Hellwig <hch@....de>
To:     dillon min <dillon.minfei@...il.com>
Cc:     Vladimir Murzin <vladimir.murzin@....com>, hch@....de,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        linux@...linux.org.uk, Kate Stewart <kstewart@...uxfoundation.org>,
        allison@...utok.net, info@...ux.net, tglx@...utronix.de,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-stm32@...md-mailman.stormreply.com,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] arm-nommu: Add use_reserved_mem() to check if
 device support reserved memory

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?