Re: [PATCH v4 07/19] spapr: Formalize notion of active interrupt controller

[David Gibson]

On Wed, Oct 09, 2019 at 11:19:26AM +0200, Cédric Le Goater wrote:
> On 09/10/2019 08:08, David Gibson wrote:
> > spapr now has the mechanism of constructing both XICS and XIVE instances of
> > the SpaprInterruptController interface.  However, only one of the interrupt
> > controllers will actually be active at any given time, depending on feature
> > negotiation with the guest.  This is handled in the current code via
> > spapr_irq_current() which checks the OV5 vector from feature negotiation to
> > determine the current backend.
> > 
> > Determining the active controller at the point we need it like this
> > can be pretty confusing, because it makes it very non obvious at what
> > points the active controller can change.  This can make it difficult
> > to reason about the code and where a change of active controller could
> > appear in sequence with other events.
> > 
> > Make this mechanism more explicit by adding an 'active_intc' pointer
> > and an explicit spapr_irq_update_active_intc() function to update it
> > from the CAS state.  We also add hooks on the intc backend which will
> > get called when it is activated or deactivated.
> > 
> > For now we just introduce the switch and hooks, later patches will
> > actually start using them.
> > 
> > Signed-off-by: David Gibson <address@hidden>
> > Reviewed-by: Greg Kurz <address@hidden>
> Btw, we will need an extra xive2 pointer for the Power10 interrupt 
> controller.

Yeah, I figured.  I think it should be easier to add more irq backends
with the new structure.

-- 
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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