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Re: [PATCH qemu v6 1/6] ppc: Start CPU in the default mode which is big-

From: David Gibson
Subject: Re: [PATCH qemu v6 1/6] ppc: Start CPU in the default mode which is big-endian 32bit
Date: Thu, 13 Feb 2020 14:34:51 +1100

On Thu, Feb 13, 2020 at 02:09:17PM +1100, Alexey Kardashevskiy wrote:
> On 12/02/2020 16:43, David Gibson wrote:
> > On Mon, Feb 03, 2020 at 02:29:38PM +1100, Alexey Kardashevskiy wrote:
> >> At the moment we enforce 64bit mode on a CPU when reset. This does not
> >> make difference as SLOF or Linux set the desired mode straight away.
> >> However if we ever boot something other than these two,
> >> this might not work as, for example, GRUB expects the default MSR state
> >> and does not work properly.
> >>
> >> This removes setting MSR_SF from the PPC CPU reset.
> > 
> > Hrm.  This is in the core cpu model so it doesn't just affect pseries,
> > but powernv (and theoretically others) as well.  Generally the cpu
> > model should have the bare metal behaviour, and we can override it in
> > the pseries machine if necessary.
> > 
> > So for a bare metal POWER system, what mode do we start in?  I'm
> > guessing it probably doesn't matter in practice, since the skiboot
> > firmware also probably does a mode set on entry, but it'd be nice to
> > get this right in theory.
> Huh. "Figure 65.  MSR setting due to interrupt" of PowerISA 3.0 says
> "The SF bit is set to 1" so after all the existing behavior is correct
> and my patch is just wrong. Cool.

Well, I guess SF after interrupt isn't *necessarily* the same as SF at
reset, but it's a good place to start.

David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!

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