Re: roms/SLOF: crashes on G5 (970) with newer pseries

[Greg Kurz]

On Mon, 12 Apr 2021 09:42:23 -0700
Jake Hamby <jake.hamby@gmail.com> wrote:

> I've been testing QEMU + KVM-PR on a Power Mac G5 Quad, and it runs
> better than I expected, but with a few glitches. The first one I
> discovered: the SLOF ROM has been compiled for POWER7 or newer, and it
> crashes when run on a G5 (KVM and TCG) if the pseries version is set
> to 2.6 or higher. The xHCI SLOF driver crashes the guest with
> pseries-2.6, and it doesn't even get to initializing the screen with
> higher versions.
> 
> Fortunately, it was a small change to recompile SLOF from source with
> the target set to "ppc970" instead of "ppcp7". I had to fix a few
> build errors first. Commit link (I would paste the patches inline, but
> I don't have Gmail set up for that yet):
> 
> https://github.com/jhamby/SLOF/commit/4ae9a012a2cec4a1b476c1b4a3933def5ae36f2b
> 
> And my commit to change the default QEMU board type to ppc970:
> 
> https://github.com/jhamby/SLOF/commit/619539cfa3a37f9527ae382cdb7573de7fa6d836
> 
> With these changes, the compiled slof.bin works perfectly for me with
> pseries versions up to 4.2 (the highest version I tried that doesn't
> expect CPU capabilities that the G5 doesn't have) and the 970mp CPU
> type (with both KVM-PR and TCG).
> 

Not sure with KVM PR but with TCG, you may select a much more modern
CPU type such as POWER9 and run the latest pseries machine type.

> I don't know if there are any negative performance implications of
> compiling SLOF for PPC 970 and using it with later CPU types, but I'm

Not sure what is the overall impact in SLOF but I doubt such a change
would be acceptable upstream.

Cc'ing Alexey (SLOF maintainer and old backpacker on POWER
virtualization) for more details.


> guessing that PowerNV is the preferred machine type for POWER8 and

PowerNV is the bare-metal "non-virtualized" machine type, probably
not what you want. The machine type for virtualization is pseries.

> newer now. It does feel like a bug that the SLOF ROM crashes
> unexpectedly with older CPU models in legal machine configurations.


Upstream QEMU+SLOF officially support pseries with a POWER8 or newer
server grade processor. Things might work with some older CPU types
but no guarantees.

> 
> Regards,
> Jake
> 

Cheers,

--
Greg