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

[Michael Ellerman]

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.

cheers