Re: [PATCH 16/67] powerpc: rename dma_direct_ to dma_nommu_

[Geert Uytterhoeven]

Hi Michael,

On Wed, Jan 3, 2018 at 7:24 AM, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
> Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> writes:
>
>> On Tue, Jan 2, 2018 at 10:45 AM, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote:
>>> Christoph Hellwig <hch@xxxxxx> 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@xxxxxxxxxxxxxx

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