On Wed, Mar 16, 2011 at 05:43:55PM +0100, Alexander Graf wrote:
> On 03/16/2011 05:57 AM, David Gibson wrote:
> >From: Ben Herrenschmidt<b...@kernel.crashing.org>
> >
> >Usually, PAPR virtual IO devices use a virtual IOMMU mechanism, TCEs,
> >to mediate all DMA transfers. While this is necessary for some sorts of
> >operation, it can be complex to program and slow for others.
> >
> >This patch implements a mechanism for bypassing TCE translation, treating
> >"IO" addresses as plain (guest) physical memory addresses. This has two
> >main uses:
> > * Simple, but 64-bit aware programs like firmwares can use the VIO devices
> >without the complexity of TCE setup.
> > * The guest OS can optionally use the TCE bypass to improve performance in
> >suitable situations.
> >
> >The mechanism used is a per-device flag which disables TCE translation.
> >The flag is toggled with some (hypervisor-implemented) RTAS methods.
>
> Is this an official extension used by anyone or is it your own
> invention that's not implemented in pHyp?
The latter.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
