linux-kernel - Re: cleanup the dma

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Message-ID: <20190824223449.GC21729@lst.de>
Date:   Sun, 25 Aug 2019 00:34:49 +0200
From:   Christoph Hellwig <hch@....de>
To:     Paul Burton <paul.burton@...s.com>
Cc:     Christoph Hellwig <hch@....de>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Guan Xuetao <gxt@....edu.cn>,
        Shawn Anastasio <shawn@...stas.io>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        James Hogan <jhogan@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-m68k@...ts.linux-m68k.org" <linux-m68k@...ts.linux-m68k.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: cleanup the dma_pgprot handling

On Fri, Aug 23, 2019 at 09:58:04PM +0000, Paul Burton wrote:
> So I believe uncached & uncached accelerated are another case like that
> described above - they're 2 different CCAs but the same "access type",
> namely uncached.
> 
> Section 4.9 then goes on to forbid mixing access types, but not CCAs.
> 
> It would be nice if the precise mapping from CCA to access type was
> provided, but I don't see that anywhere. I can check with the
> architecture team to be sure, but to my knowledge we're fine to mix
> access via kseg1 (ie. uncached) & mappings with CCA=7 (uncached
> accelerated).

Ok.  Looks like we can keep it then and I'll add a comment to the
code with the above reference.