Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device

On Tue, Mar 24, 2020 at 02:05:54PM +1100, Alexey Kardashevskiy wrote:

This is for persistent memory which you can DMA to/from but yet it does
not appear in the system as a normal memory and therefore requires
special handling anyway (O_DIRECT or DAX, I do not know the exact
mechanics). All other devices in the system should just run as usual,
i.e. use 1:1 mapping if possible.

On other systems (x86 and arm) pmem as long as it is page backed does
not require any special handling.  This must be some weird way powerpc
fucked up again, and I suspect you'll have to suffer from it.