[PATCH RESEND v2 0/8] Cache-coherent DMA access using UIO

[arnd@arndb.de (Arnd Bergmann)]

On Monday, August 8, 2016 11:22:29 AM CEST Anup Patel wrote:
> The goal of this patchset is to improve UIO framework and UIO dmem
> driver to allow cache-coherent DMA accesses from user-space.
> 
> This patchset is based on two previous patchsets:
> 1) [PATCH v5 0/6] UIO driver for APM X-Gene QMTM
> (Refer, http://www.spinics.net/lists/devicetree/msg58244.html)
> 2) [PATCH 0/4] Fix and extend uio_dmem_genirq
> (Refer, https://lkml.org/lkml/2016/5/17/141)
> 
> We have adopted only patch0-3 of patchset1 which was abandoned
> long time back. We have taken care of last few unaddressed comments
> on these patches.
> 
> The patchset2 is quite recent has been adopted entirely. We have
> taken care review comments on these patches too.
> 
> This patchset is based on v4.7-rc7 tag and it is available in uio-v2
> branch of https://github.com/Broadcom/arm64-linux.git


UIO devices are generally meant to be things that do not
perform DMA and that don't screw up the rest of the system
when misused. A device that is able to access any physical
memory doesn't belong into this category. The way that
uio_dmem_genirq.c gets around this is by requiring the device
to be created by some code that sets up a separate IOMMU
domain first, but the DT probing here doesn't do that.
Note that IOMMU domains typically use 32-bit addressing,
so the entire "dma_mask from property" dance isn't even
required.

Also, this seems to duplicate a lot of the work that
went into "vfio". Can you explain why we need another way
of doing the same thing here?

	Arnd