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

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