Re: [Linaro-mm-sig] [RFCv3 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms

Arnd Bergmann
2015-02-03T16:37:59Z

On Tuesday 03 February 2015 11:22:01 Rob Clark wrote:
> On Tue, Feb 3, 2015 at 11:12 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> > I agree for the case you are describing here. From what I understood
> > from Rob was that he is looking at something more like:
> >
> > Fig 3
> > CPU--L1cache--L2cache--Memory--IOMMU---<iobus>--device
> >
> > where the IOMMU controls one or more contexts per device, and is
> > shared across GPU and non-GPU devices. Here, we need to use the
> > dmap-mapping interface to set up the IO page table for any device
> > that is unable to address all of system RAM, and we can use it
> > for purposes like isolation of the devices. There are also cases
> > where using the IOMMU is not optional.
>
>
> Actually, just to clarify, the IOMMU instance is specific to the GPU..
> not shared with other devices. Otherwise managing multiple contexts
> would go quite badly..
>
> But other devices have their own instance of the same IOMMU.. so same
> driver could be used.

I think from the driver perspective, I'd view those two cases as
identical. Not sure if Russell agrees with that.

Arnd