Re: [Qemu-devel] [PATCH 00/10] Fix versatile_pci (and break versatilepb linux guests!)

[Aurelien Jarno <aurelien@aurel32.net>]

On Sun, Mar 24, 2013 at 04:49:37PM +0000, Peter Maydell wrote:
> On 24 March 2013 15:58, Aurelien Jarno <aurelien@aurel32.net> wrote:
> > On Sun, Mar 24, 2013 at 11:32:30AM +0000, Peter Maydell wrote:
> >> This patch series fixes a number of serious bugs in our emulation of
> >> the PCI controller found on VersatilePB and the early Realview boards:
> 
> >> Patchset tested on both versatilepb and realview, using a set of
> >> Linux kernel patches written by Arnd Bergmann:
> >> http://lists.infradead.org/pipermail/linux-arm-kernel/2010-October/029040.html
> >> which were in turn tested against real PB926 and PB1176 hardware.
> >>
> >>
> >>  * WARNING WARNING *
> >>
> >> This patchset will break any use of PCI (including the default SCSI
> >> card) on versatilepb with current Linux kernels, because those kernels
> >
> > Do you mean Versatile/PB and not Versatile/AB, or actually both?
> 
> I mean PB. The AB doesn't have a PCI controller (though we incorrectly
> model it as having one; I suppose we could patch QEMU to stop doing
> that).
> 
> >> have the matching bug in interrupt mapping to old QEMU.
> >
> > How is real hardware working with this bug?
> 
> It doesn't. Unless you apply Arnd's patches, PCI support
> on real hardware is flat out broken. (This was never noticed
> because (a) real hardware is getting rare by now and (b) the
> PCI backplane is even rarer.)
> 
> >> I've provided a property for enabling the old broken IRQ mapping;
> >> this can be enabled with the command line option:
> >>       -global versatile_pci.broken-irq-mapping=1
> >>
> >> (If anybody wants to suggest a better way of handling this please do.)
> >
> > Do you have a pointer to the corresponding kernel patch? Is it possible
> > to get the kernel to detect if it should use the correct or the broken
> > IRQ mapping?
> 
> I linked to the kernel patches above. It might I guess be possible
> to identify a fixed QEMU (if nothing else we could put something
> into QEMU that was identifiable); that still leaves existing kernels
> breaking, though.
> 

Now that stable kernel releases work well and that most distribution are
basing their releases on longterm kernels, it might be possible to get
the fix included there, and from there in the distributions. I think
it's something that would be acceptable, provided it is below the 100
lines limit including context.

-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net