On 10/07/18 19:02, Christoph Hellwig wrote:

quoted

These patches attempt to deal with this in the simplest way possible by
generalising the specific quirk for 32-bit bridges into an arbitrary
mask which can then also be plumbed into the firmware code. In the
interest of being minimally invasive, I've only included a point fix
for the IOMMU issue as seen on arm64 - there may be further tweaks
needed in DMA ops to catch all possible incarnations of this problem,
but this initial RFC is mostly about the impact beyond the dma-mapping
subsystem itself.

Thanks, this looks very nice to me.

In fact it probably solves the RISC-V/Xiling problem as well if we can
just add the dma-ranges property to the device tree for the affected
systems.  Palmer, do you know how easily the DT could be updated for
that case?

That would indeed be nice, but beware that the way PCI devices are 
bodged through of_dma_configure() only actually works for dma-coherent 
and is busted WRT parsing dma-ranges correctly. Fixing that is my next 
step after getting these basics done ;)

Robin.