Re: [Qemu-devel] [QEMU-PPC] [PATCH 1/4] target/ppc/spapr: Add SPAPR_CAP_LARGE_DECREMENTER

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Feb 26, 2019 at 05:26:10PM +1100, Suraj Jitindar Singh wrote:
> On Tue, 2019-02-26 at 14:39 +1100, David Gibson wrote:
> > On Tue, Feb 26, 2019 at 02:05:28PM +1100, Suraj Jitindar Singh wrote:
> > > Add spapr_cap SPAPR_CAP_LARGE_DECREMENTER to be used to control the
> > > availability and size of the large decrementer made available to
> > > the
> > > guest.
> > > 
> > > Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
> > > ---
> > >  hw/ppc/spapr.c         |  2 ++
> > >  hw/ppc/spapr_caps.c    | 45
> > > +++++++++++++++++++++++++++++++++++++++++++++
> > >  include/hw/ppc/spapr.h |  5 ++++-
> > >  3 files changed, 51 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index b6a571b6f1..acf62a2b9f 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -2077,6 +2077,7 @@ static const VMStateDescription vmstate_spapr
> > > = {
> > >          &vmstate_spapr_irq_map,
> > >          &vmstate_spapr_cap_nested_kvm_hv,
> > >          &vmstate_spapr_dtb,
> > > +        &vmstate_spapr_cap_large_decr,
> > >          NULL
> > >      }
> > >  };
> > > @@ -4288,6 +4289,7 @@ static void
> > > spapr_machine_class_init(ObjectClass *oc, void *data)
> > >      smc->default_caps.caps[SPAPR_CAP_IBS] = SPAPR_CAP_BROKEN;
> > >      smc->default_caps.caps[SPAPR_CAP_HPT_MAXPAGESIZE] = 16; /*
> > > 64kiB */
> > >      smc->default_caps.caps[SPAPR_CAP_NESTED_KVM_HV] =
> > > SPAPR_CAP_OFF;
> > > +    smc->default_caps.caps[SPAPR_CAP_LARGE_DECREMENTER] = 0;
> > 
> > This looks basically fine, but the name kind of suggests it's a
> > boolean, whereas it's actually a number of bits.  I wonder if just
> > calling it "decrementer bits" would be clearer, with it defaulting to
> > 32.
> 
> Yes, except there's a difference between a decrementer with 32 bits and
> a large decrementer with 32 bits...

Ok, and that difference is..?

> SPAPR_CAP_LARGE_DECR_NR_BITS?

That could work.

-- 
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_!
http://www.ozlabs.org/~dgibson

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