[PATCH 08/20] powerpc/dma: remove the unused dma_nommu_ops export

[Benjamin Herrenschmidt]

On Wed, 2018-08-22 at 08:45 +0200, Christoph Hellwig wrote:
> On Thu, Aug 09, 2018 at 10:01:16AM +1000, Benjamin Herrenschmidt wrote:
> > On Tue, 2018-07-31 at 14:16 +0200, Christoph Hellwig wrote:
> > > It turns out cxl actually uses it.  So for now skip this patch,
> > > although random code in drivers messing with dma ops will need to
> > > be sorted out sooner or later.
> > 
> > CXL devices are "special", they bypass the classic iommu in favor of
> > allowing the device to operate using the main processor page tables
> > using an MMU context (so basically the device can use userspace
> > addresses directly), akin to ATS.
> > 
> > I think the code currently uses the nommu ops as a way to do a simple
> > kernel mapping for kernel drivers using CXL (not userspace stuff)
> > though.
> 
> Its still a horrible idea to have this in drivers/, we need some
> core API to mediate this behavior.  Also if the device supports
> using virtual addresses dma_nommu_ops seems wrong as it won't do
> the right thing for e.g. vmalloc addresses not mapped into the
> kernel linear mapping (which I guess can't currently happen on
> powerpc, but still..)

You are right it won't do the right thing, but neither will standard
DMA ops, will they ? Drivers know not to try to dma_map vmalloc
addresses without first getting the underlying page, nothing unusal
there.

Yes I agree having this in drivers somewhat sucks though.

Cheers,
Ben.