linux-kernel - Re: [PATCH 16/67] powerpc: rename dma_direct_ to dma_nommu

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Date:   Wed, 3 Jan 2018 19:19:46 +1100
From:   Julian Calaby <julian.calaby@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Christoph Hellwig <hch@....de>,
        iommu@...ts.linux-foundation.org,
        Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
        linux-ia64@...r.kernel.org,
        Linux-sh list <linux-sh@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        Guan Xuetao <gxt@...c.pku.edu.cn>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linux-c6x-dev@...ux-c6x.org,
        "open list:QUALCOMM HEXAGON..." <linux-hexagon@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        arcml <linux-snps-arc@...ts.infradead.org>,
        adi-buildroot-devel@...ts.sourceforge.net,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        patches@...ups.riscv.org,
        "open list:METAG ARCHITECTURE" <linux-metag@...r.kernel.org>,
        "Mailing List, Arm" <linux-arm-kernel@...ts.infradead.org>,
        Michal Simek <monstr@...str.eu>,
        Parisc List <linux-parisc@...r.kernel.org>,
        Cris <linux-cris-kernel@...s.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        alpha <linux-alpha@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 16/67] powerpc: rename dma_direct_ to dma_nommu_

Hi All,

On Wed, Jan 3, 2018 at 6:49 PM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> Hi Michael,
>
> On Wed, Jan 3, 2018 at 7:24 AM, Michael Ellerman <mpe@...erman.id.au> wrote:
>> Geert Uytterhoeven <geert@...ux-m68k.org> writes:
>>
>>> On Tue, Jan 2, 2018 at 10:45 AM, Michael Ellerman <mpe@...erman.id.au> wrote:
>>>> Christoph Hellwig <hch@....de> writes:
>>>>
>>>>> We want to use the dma_direct_ namespace for a generic implementation,
>>>>> so rename powerpc to the second best choice: dma_nommu_.
>>>>
>>>> I'm not a fan of "nommu". Some of the users of direct ops *are* using an
>>>> IOMMU, they're just setting up a 1:1 mapping once at init time, rather
>>>> than mapping dynamically.
>>>>
>>>> Though I don't have a good idea for a better name, maybe "1to1",
>>>> "linear", "premapped" ?
>>>
>>> "identity"?
>>
>> I think that would be wrong, but thanks for trying to help :)
>>
>> The address on the device side is sometimes (often?) offset from the CPU
>> address. So eg. the device can DMA to RAM address 0x0 using address
>> 0x800000000000000.
>>
>> Identity would imply 0 == 0 etc.
>>
>> I think "bijective" is the correct term, but that's probably a bit
>> esoteric.
>
> OK, didn't know about the offset.
> Then "linear" is what we tend to use, right?

If this is indeed a linear mapping, can we just remove this and
replace it with the new "generic" mapping being introduced by this
patchset?

Thanks,

-- 
Julian Calaby

Email: julian.calaby@...il.com
Profile: http://www.google.com/profiles/julian.calaby/