provide in-place uncached remapping for dma-direct (resend)

From: Christoph Hellwig
Date: Thu Feb 20 2020 - 12:02:03 EST

Hi all,

this series provides support for remapping places uncached in-place in
the generic dma-direct code, and moves openrisc over from its own
in-place remapping scheme. The arm64 folks also had interest in such
a scheme to avoid problems with speculating into cache aliases.

Also all architectures that always use small page mappings for the
kernel and have non-coherent DMA should look into enabling this
scheme, as it is much more efficient than the vmap remapping.