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.
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