[parisc-linux] ZONE_DMA

[Alan Cox]

> > EISA on PC can hit the full 32bits. DMA is meant to indicate the 16Mb lowest
> > memory segment that ISA can hit (which may not be at 0 depending on the box)
> 
> OK, so people who write EISA drivers are not going to specify GFP_DMA.
> Or shouldn't.

Or know something about their hardware being crap.

> > Some PCI cards have the same limit 8)
> But that's handled through the PCI DMA mapping interface these days.

Yes

> So how should we be populating our zones?  Put all of our memory in
> ZONE_DMA, like ppc, since the only people who'll be specifying GFP_DMA
> will have done so incorrectly?  Put the first 16MB of it in there,

That is a very dangerous assumption (as some PPC people have discovered when
they DMA stuff into the wrong place)

> since we might support ISA some day?  Put none of it in there on the
> grounds we don't support ISA at all?

I think none is safer. pci_alloc_consistent seems to address all the stuff
we worry about. 

Alan