Re: [Qemu-devel] [PATCH v3 06/13] pc: apic_common: extend APIC ID property to 32bit

[Igor Mammedov]

On Tue, 18 Oct 2016 10:59:17 -0200
Eduardo Habkost <address@hidden> wrote:

> On Tue, Oct 18, 2016 at 02:36:10PM +0200, Igor Mammedov wrote:
> > On Tue, 18 Oct 2016 08:56:28 -0200
> > Eduardo Habkost <address@hidden> wrote:
> >   
> > > On Thu, Oct 13, 2016 at 11:52:40AM +0200, Igor Mammedov wrote:  
> > > > ACPI ID is 32 bit wide on CPUs with x2APIC support.
> > > > Extend 'id' property to support it.
> > > > 
> > > > Signed-off-by: Igor Mammedov <address@hidden>
> > > > ---
> > > > v3:
> > > >    keep original behaviour where 'id' is readonly after
> > > >    object is realized (pbonzini)
> > > > ---    
> > > [...]  
> > > > diff --git a/hw/intc/apic_common.c b/hw/intc/apic_common.c
> > > > index 8d01c9c..30f2af0 100644
> > > > --- a/hw/intc/apic_common.c
> > > > +++ b/hw/intc/apic_common.c
> > > > @@ -428,7 +429,6 @@ static const VMStateDescription vmstate_apic_common 
> > > > = {
> > > >  };
> > > >  
> > > >  static Property apic_properties_common[] = {
> > > > -    DEFINE_PROP_UINT8("id", APICCommonState, id, -1),
> > > >      DEFINE_PROP_UINT8("version", APICCommonState, version, 0x14),
> > > >      DEFINE_PROP_BIT("vapic", APICCommonState, vapic_control, 
> > > > VAPIC_ENABLE_BIT,
> > > >                      true),
> > > > @@ -437,6 +437,49 @@ static Property apic_properties_common[] = {
> > > >      DEFINE_PROP_END_OF_LIST(),
> > > >  };
> > > >  
> > > > +static void apic_common_get_id(Object *obj, Visitor *v, const char 
> > > > *name,
> > > > +                               void *opaque, Error **errp)
> > > > +{
> > > > +    APICCommonState *s = APIC_COMMON(obj);
> > > > +    int64_t value;
> > > > +
> > > > +    value = s->apicbase & MSR_IA32_APICBASE_EXTD ? s->initial_apic_id 
> > > > : s->id;
> > > > +    visit_type_int(v, name, &value, errp);
> > > > +}    
> > > 
> > > Who exactly is going to read this property and require this logic
> > > to be in the property getter?  
> > As it's set/read only from CPU we don't actually have to expose it
> > as property.
> > However, I've kept it as read/write property because it has already
> > been this way and been exposed to external users as some magic property.
> > Not sure is anyone cares.
> > 
> >   
> > > Do we really need to expose this to the outside as a magic
> > > property that changes depending on hardware state? Returning
> > > initial_apic_id sounds much simpler.  
> > Well that's what it is now, so I've kept current behavior.
> > If we decide to change property behavior or drop it altogether
> > I can do it on top.
> >   
> 
> I agree to make them static properties as follow-up patch. This
> way, if the change breaks anything we can revert only that patch.
Static property won't work here as it should show APIC ID
depending on current CPU mode.

I could make it readonly property on respin,
and set apic.id/initial_apic_id directly from CPU.
Change would be
   - apic_common_set_id()
   + apic_common::set_apic_id() callback
It won't get us less LOC, more likely it will take even more
code to do so.
As it's in this patch, it's at least consistent in a way
values are get/set. And effectively it's readonly due to check:

+    if (dev->realized) {
+        qdev_prop_set_after_realize(dev, name, errp);
+        return;
+    }

as external user can see only realized apic device.