Re: [PATCH v4 16/19] mac_newworld: Add machine types for different mac99 configs

[Mark Cave-Ayland]

On 28/10/2022 13:18, BALATON Zoltan wrote:

> On Fri, 28 Oct 2022, Mark Cave-Ayland wrote:
> > On 25/10/2022 17:44, BALATON Zoltan wrote:
> > > The mac99 machine emulates different machines depending on machine
> > > properties or even if it is run as qemu-system-ppc64 or
> > > qemu-system-ppc. This is very confusing for users and many hours were
> > > lost trying to explain it or finding out why commands users came up
> > > with are not working as expected. (E.g. Windows users might think
> > > qemu-system-ppc64 is just the 64 bit version of qemu-system-ppc and
> > > then fail to boot a 32 bit OS with -M mac99 trying to follow an
> > > example that had qemu-system-ppc.) To avoid such confusion, add
> > > explicit machine types for the different configs which will work the
> > > same with both qemu-system-ppc and qemu-system-ppc64 and also make the
> > > command line clearer for new users.
> >
> > What was the outcome of the discussion re: having separate machines for 32-bit and 
> > 64-bit PPC targets? My understanding is the issue here was deciding what to do, 
> > rather than actually making the code changes.
>
> Who do you think will or should decide about this? There are about 3 people who care 
> about Mac emulation on this list: you, Howard and me. You already have my and 
> Howard's vote to introduce these machines types. Who else should vote or decide on 
> this? Please apply this patch now and if it causes problem it can still be dropped 
> duting the freeze but if you don't apply it now it can't get into before next spring.

This is not restricted to qemu-system-ppc though: there was a discussion (which was 
still ongoing) as to how all of QEMU should handle 32-bit and 64-bit machines i.e. 
should qemu-system-ppc64 only contain 64-bit machines and qemu-system-ppc only 
contain 32-bit machines? If we wish to make a change here, we should wait for the 
outcome of this to ensure consistency here.

> > Also what was your motivation for choosing the machine names? I see you've used 
> > powerbook for via=pmu-adb, but I think quite a few people use pmu-adb for older OS 
> > X server hardware. At the very least some pointers to reference device trees and 
> > some rationale behind the decision is needed for review.
>
> See my reply to Howard's message with some more info and links. My immediate 
> motivation was that we've lost about two days when somobody contacted me about VGA 
> pass through sending logs about all kinds of failures he got. After many logs I've 
> noticed that he was using qemu-system-ppc64 -M mac99,via=pmu thinking that on 64bit 
> host that's the executable he should use. Unfortunately the commands were not shared 
> just the logs so this took a while to notice. Also if you look at the forum Howard 
> runs you can see this problem is coming up frequently and I think the've also lost 
> countless hours due to this. It's about time to put an end on it and stop wasting 
> othet's time. As for The machines, the powermac ones are straight forward as those 
> are closest to what we emulate for G4 and G5 Mac. I've chosen the powerbook becuase 
> that's the only machine I know that had PMU and ADB but If someone knows a better 
> machine we can change this (even as bug fix during the freeze). Here's some info on 
> this powerbook: https://ppc.0penbsd.narkive.com/s49Kcx1u/x-on-powerbook-g4

In all my time working on QEMU this has happened to me once: yes, I agree it can be 
annoying but given how rare it happens I don't see a need to make a rushed decision now.

In terms of choosing the machines for QEMU we will need a full copy of the DT from 
real hardware for comparison with OpenBIOS, and ideally a Linux dmesg.


ATB,

Mark.