[OpenBIOS] [PATCH] ppc: force target CPU
mark.cave-ayland at ilande.co.uk
Mon Jan 18 20:14:15 CET 2016
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
>>> 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...?
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:
and the commit where the switch appears is here, apparently in an
attempt to find a CPU that worked at that time:
>> It is probably best if you make code that runs on 603 but is tuned
>> for (say) 750, as in -mcpu=603 -mtune=750.
Given that 603 was used in a real BeBox then this would seem to be a
reasonable default. And perhaps the QEMU PReP CPU should be updated
>>> select_prefix powerpc64
>>> - CFLAGS="-Wa,-a64 -m64 -msoft-float -fno-builtin"
>>> + CFLAGS="-Wa,-a64 -m64 -mcpu=G5 -msoft-float -fno-builtin"
>> 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.
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