Re: [Qemu-devel] [PATCH] pci: Length-align config space accesses

[Michael S. Tsirkin]

On Wed, Jul 20, 2011 at 06:18:43PM +0200, Jan Kiszka wrote:
> On 2011-07-20 18:17, Isaku Yamahata wrote:
> > On Wed, Jul 20, 2011 at 04:27:08PM +0200, Jan Kiszka wrote:
> >> On 2011-07-20 14:15, Jan Kiszka wrote:
> >>> On 2011-07-20 14:00, Isaku Yamahata wrote:
> >>>> Hi. This clean up looks good basically.
> >>>
> >>> Oops, forgot to cc you. Sorry.
> >>>
> >>>> But when conventional pci device is accessed via MMCONFIG area,
> >>>> addr &= addr_mask doesn't work as expected.
> >>>> The config area of [256, 4K) of conventional pci should have no effect.
> >>>
> >>> Mmh, I see. Looks like we need to split accesses at this boundary and
> >>> executed them separately.
> >>
> >> Nope, no such issue: we already automatically split up accesses that
> >> span the legacy/extended boundary. Just like so far, legacy config space
> >> handlers have to filter out requests that address regions >= 256.
> > 
> > For example, when accessing to offset 257 of conventional pci device,
> > the access is routed to offset 1 due to the masking.
> > Such overwrapping isn't correct.
> 
> No, it isn't routed like that. The mask used via mmio is 0xfff.
> 
> Jan

I thought about this some more, I'd like to see how devices
are going to benefit. Any examples?
If not, is it easier to simply make this logic
part of dev assignment?


> -- 
> Siemens AG, Corporate Technology, CT T DE IT 1
> Corporate Competence Center Embedded Linux