[Linaro-mm-sig] [PATCH 4/8] dma-buf: add peer2peer flag

Thierry Reding treding at nvidia.com
Wed Apr 25 07:43:38 UTC 2018

On Wed, Apr 25, 2018 at 12:09:05AM -0700, Christoph Hellwig wrote:
> On Wed, Apr 25, 2018 at 09:02:17AM +0200, Daniel Vetter wrote:
> > Can we please not nack everything right away? Doesn't really motivate
> > me to show you all the various things we're doing in gpu to make the
> > dma layer work for us. That kind of noodling around in lower levels to
> > get them to do what we want is absolutely par-for-course for gpu
> > drivers. If you just nack everything I point you at for illustrative
> > purposes, then I can't show you stuff anymore.
> No, it's not.  No driver (and that includes the magic GPUs) has
> any business messing with dma ops directly.
> A GPU driver imght have a very valid reason to disable the IOMMU,
> but the code to do so needs to be at least in the arch code, maybe
> in the dma-mapping/iommu code, not in the driver.
> As a first step to get the discussion started we'll simply need
> to move the code Thierry wrote into a helper in arch/arm and that
> alone would be a massive improvement.  I'm not even talking about
> minor details like actually using arm_get_dma_map_ops instead
> of duplicating it.
> And doing this basic trivial work really helps to get this whole
> mess under control.

That's a good idea and I can prepare patches for this, but I'd like to
make those changes on top of the fix to keep the option of getting this
into v4.16 if at all possible.

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