Re: [PATCH v3 0/6] Prerequisites for NXP LS104xA SMMU enablement

[Robin Murphy]

On 31/05/2019 18:08, Christoph Hellwig wrote:
> On Fri, May 31, 2019 at 06:03:30PM +0100, Robin Murphy wrote:
> > > The thing needs to be completely redone as it abuses parts of the
> > > iommu API in a completely unacceptable way.
> >
> > `git grep iommu_iova_to_phys drivers/{crypto,gpu,net}`
> >
> > :(
> >
> > I guess one alternative is for the offending drivers to maintain their own
> > lookup tables of mapped DMA addresses - I think at least some of these
> > things allow storing some kind of token in a descriptor, which even if it's
> > not big enough for a virtual address might be sufficient for an index.
>
> Well, we'll at least need DMA API wrappers that work on the dma addr
> only and hide this madness underneath.  And then tell if an given device
> supports this and fail the probe otherwise.

Bleh, I'm certainly not keen on formalising any kind of 
dma_to_phys()/dma_to_virt() interface for this. Or are you just 
proposing something like dma_unmap_sorry_sir_the_dog_ate_my_homework() 
for drivers which have 'lost' the original VA they mapped?

Robin.