Geert Uytterhoeven [off-list ref] writes:

On Tue, Jan 2, 2018 at 10:45 AM, Michael Ellerman [off-list ref] wrote:

quoted

Christoph Hellwig [off-list ref] writes:

quoted

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