[OpenBIOS] [PATCH] ppc: force target CPU

[Segher Boessenkool]

On Mon, Jan 18, 2016 at 07:29:33PM +0100, 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...?

I would use 603.  601 is problematic (it is not fully PowerPC).  602 for
all intents and purposes does not exist; also is problematic for a few
things (no DP float insns, no available manual, etc.)

> > G5 is 970.  It includes VMX (AltiVec) vector support; you may want to
> > aim lower here too, say, power4.
> 
> Why? QEMU's pseries emulation uses SLOF instead of OpenBIOS, and ppc64
> mac99 uses a 970fx by default.

970 is the only 64-bit CPU ever used in Macs, sure.  There are later CPUs
that do not have VMX (e.g. power5).  -mcpu=970 -mno-altivec is essentially
the same as -mcpu=power4.


Segher