Re: Xen and bounce buffers

[Manuel Bouyer <bouyer%antioche.lip6.fr@localhost>]

On Thu, Jan 20, 2005 at 06:56:56AM -0800, Jason Thorpe wrote:
> 
> On Jan 20, 2005, at 4:31 AM, Manuel Bouyer wrote:
> 
> >Log Message:
> >bus_dma(9) for xen. Derived from arch/x86/x86/bus_dma.c.
> >bounce buffers not supported yet, because xen doesn't have an interface
> >to request memory in a specific range (this means that DMA on ISA won't
> >be supported), but I've left the code commented out because xen will
> >likely provide an appropriate hypercall in the future.
> 
> This is important for more than just ISA DMA.  PCI DMA needs them on 
> systems with more than 4G of RAM, if the device doesn't support dual 
> address cycle.

Sure. This is why the xen folk will probably add an hypercall to
allocate DMA-safe memory. Otherwise 32bit PCI won't work on x86_64.
I talked with Christian about this, he said that this would most likely
be something similar to what is currently done to get contigous memory
(we give some pages to the hypervisor, which returns us the same amount
of memory, but contiguous).

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--