[PATCH 01/20] kernel/dma/direct: take DMA offset into account in dma_direct_supported

[Benjamin Herrenschmidt]

On Thu, 2018-08-23 at 07:24 +0200, Christoph Hellwig wrote:
> > Well, iommus can have bypass regions, which we also use for
> > performance, so we do at dma_set_mask() time "swap" the ops around, and
> > in that case, we do want to check the mask against the actual top of
> > memory...
> 
> That is a bit of a powerpc special case (we also had one other arch
> doing that, but it got removed in the great purge, can't rember which
> one right now).  Everyone else has one set of ops, and they just switch
> to the direct mapping inside the iommu ops.

We more or less do that too in some of ours these days bcs of the whole
coherent_mask vs mask where a given device might need either depending
on the type of mapping.

Ben.