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

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Date:   Wed, 3 Jan 2018 08:49:35 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     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>,
        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 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?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds