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

[Julian Calaby <julian.calaby@xxxxxxxxx>]

Hi All,

On Wed, Jan 3, 2018 at 6:49 PM, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> 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?

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