On Thu, Jun 17, 2021 at 7:07 PM Christoph Hellwig [off-list ref] wrote:

On Thu, Jun 17, 2021 at 06:40:58PM +0900, Tomasz Figa wrote:

quoted

Sorry, I meant dma_alloc_attrs() and yes, it's indeed a misnomer. Our
use case basically has no need for the additional coherent mapping, so
creation of it can be skipped to save some vmalloc space. (Yes, it
probably only matters for 32-bit architectures.)

Yes, that is the normal use case, and it is solved by using
dma_alloc_noncoherent or dma_alloc_noncontigous without the vmap
step.

True, silly me. Probably not enough coffee at the time I was looking at it.

With that, wouldn't it be possible to completely get rid of
dma_alloc_{coherent,attrs}() and use dma_alloc_noncontiguous() +
optional kernel and/or userspace mapping helper everywhere? (Possibly
renaming it to something as simple as dma_alloc().