Re: [OpenBIOS] [PATCH] ppc: force target CPU

[Andreas Färber]

Am 18.01.2016 um 20:14 schrieb Mark Cave-Ayland:
> On 18/01/16 18:29, Andreas Färber wrote:
> > Am 18.01.2016 um 07:40 schrieb Segher Boessenkool:
> > > On Tue, Dec 29, 2015 at 04:43:09PM +0000, Mark Cave-Ayland wrote:
> > > > After some further research, there are currently 2 reasons that make me
> > > > feel we should be targeting earlier CPUs than the G3 for 32-bit OpenBIOS
> > > > builds: firstly there are some people trying to emulate PPC 604 CPUs
> > > > with QEMU/KVM which currently hangs in OpenBIOS, and secondly there has
> > > > been talk of switching over QEMU's PReP machine from OHW to OpenBIOS
> > > > instead.
> > > >
> > > > To that end the minimum supported CPU for PPC needs to be 602 and so
> > > > with this in mind, I've lightly tested the attached patch which seems to
> > > > work here - Cole, does this work on your compiler setup? If so, I think
> > > > this is the option I would like to apply upstream.
> > >
> > > I seriously doubt you have a 602 anywhere, or an emulator for it even.
> > > You want 603/604, which were both called "G2".
> >
> > For reasons unknown to me as current maintainer, QEMU's PReP machine
> > uses a "602" CPU model by default. We are aware of issues with that
> > default and have overridden it from the command line occasionally in our
> > testing, but did not reach broader agreement on why and what to change
> > it to... so if you have more input on that...?
> >
> > http://git.qemu-project.org/?p=qemu.git;a=blob;f=hw/ppc/prep.c;h=0e102fcfbe0...
>
> You can see this if you go further back in history before the files were
> moved; it seems like Jocelyn Mayer switched to a 604 in order to fix OS/2:
>
> http://git.qemu-project.org/?p=qemu.git;a=commitdiff;h=da9b266bb8491fd41badf...
>
> and the commit where the switch appears is here, apparently in an
> attempt to find a CPU that worked at that time:
>
> http://git.qemu-project.org/?p=qemu.git;a=commitdiff;h=b37fc148bb81b5b022846...

I don't really care what Jocelyn played around with. Either there was a
real 602 based PReP machine or there wasn't. If there was, we should
take the earliest -mcpu setting like you suggested; if there was no such
machine, then we can fix QEMU and take up Segher's suggestion.

Regards,
Andreas