question about dma-ranges

[David Gibson]

On Tue, Oct 26, 2010 at 08:37:55PM -0500, Timur Tabi wrote:
> On Tue, Oct 26, 2010 at 7:51 PM, Mitch Bradley <wmb at firmworks.com> wrote:
> >  It's probably unnecessary on modern machines, but old PCs were fairly
> > restrictive about DMA addresses due to short counters.  The buses on which
> > such restrictions applied are no longer at the root level, but they were
> > once there...
> 
> It's still necessary.  The QE, which we ship on several of our current
> parts, can only DMA to/from 32-bit addresses, even on SOCs that
> support 36-bit addressing for everything else.

But the QE is not at the top-level, IIRC, so its restrictions can be
encoded in the dma-ranges on its own bus.  We're talking specifically
about the special case of dma-ranges in the root node, not the utility
of dma-ranges in general which is clear.

-- 
David Gibson			| I'll have my music baroque, and my code
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				| _way_ _around_!
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