Re: [PATCH 1/6] spapr: Add an "spapr" property to sPAPR CPU core

[Eduardo Habkost]

On Wed, Dec 09, 2020 at 09:24:36PM +0100, Greg Kurz wrote:
> On Wed, 9 Dec 2020 13:26:17 -0500
> Eduardo Habkost <ehabkost@redhat.com> wrote:
> 
> > On Wed, Dec 09, 2020 at 07:11:40PM +0100, Philippe Mathieu-Daudé wrote:
> > [...]
> > > >>>> @@ -200,7 +199,7 @@ static void spapr_cpu_core_reset(DeviceState 
> > > >>>> *dev)
> > > >>>>      int i;
> > > >>>>  
> > > >>>>      for (i = 0; i < cc->nr_threads; i++) {
> > > >>>> -        spapr_reset_vcpu(sc->threads[i]);
> > > >>>> +        spapr_reset_vcpu(sc->threads[i], sc->spapr);
> > > >>>
> > > >>> Why reset() needs access to the machine state, don't
> > > >>> you have it in realize()?
> > > >>>
> > > >>
> > > >> This is for the vCPU threads of the sPAPR CPU core. They don't have the
> > > >> link to the machine state.
> > > > 
> > > > They are created by spapr_create_vcpu() + spapr_realize_vcpu() in
> > > > spapr_cpu_core_realize(), which has sc->spapr set... Am I missing
> > > > something?
> > > 
> > > Anyhow, from a QOM design point of view, resetfn() is not the correct
> > > place to set a property IMHO, so Cc'ing Eduardo.
> > 
> > This patch is not setting the property on resetfn(), it is
> > setting it on CPU core pre_plug().
> > 
> > This is more complex than simply using qdev_get_machine() and I
> > don't see why it would be better, but I don't think it's wrong.
> > 
> 
> The reference to the machine state is basically needed to
> setup/reset/teardown interrupt presenters in the IRQ chip
> backend. It is a bit unfortunate to express this dependency
> at realize(), reset() and unrealize(). Maybe having an
> "irq_chip" property linked to the IRQ chip backend would
> make more sense ?
> 

Considering that the spapr_irq_*() functions get a
SpaprMachineState argument and deal with two interrupt
controllers, maybe you won't be able to save what you need in a
single irq_chip field?

I don't have a strong opinion here.  It feels weird to me to save
a reference to the global machine object that is always
available, but I don't think that's a problem if you believe the
resulting code looks better.

-- 
Eduardo