spapr: Formalize notion of active interrupt controller

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 <david@gibson.dropbear.id.au>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>

hw/ppc/spapr_irq.c

@@ -586,6 +586,7 @@ qemu_irq spapr_qirq(SpaprMachineState *spapr, int irq)
 
 int spapr_irq_post_load(SpaprMachineState *spapr, int version_id)
 {
+    spapr_irq_update_active_intc(spapr);
     return spapr->irq->post_load(spapr, version_id);
 }
 
@@ -593,6 +594,8 @@ void spapr_irq_reset(SpaprMachineState *spapr, Error **errp)
 {
     assert(!spapr->irq_map || bitmap_empty(spapr->irq_map, spapr->irq_map_nr));
 
+    spapr_irq_update_active_intc(spapr);
+
     if (spapr->irq->reset) {
         spapr->irq->reset(spapr, errp);
     }
@@ -619,6 +622,54 @@ int spapr_irq_get_phandle(SpaprMachineState *spapr, void *fdt, Error **errp)
     return phandle;
 }
 
+static void set_active_intc(SpaprMachineState *spapr,
+                            SpaprInterruptController *new_intc)
+{
+    SpaprInterruptControllerClass *sicc;
+
+    assert(new_intc);
+
+    if (new_intc == spapr->active_intc) {
+        /* Nothing to do */
+        return;
+    }
+
+    if (spapr->active_intc) {
+        sicc = SPAPR_INTC_GET_CLASS(spapr->active_intc);
+        if (sicc->deactivate) {
+            sicc->deactivate(spapr->active_intc);
+        }
+    }
+
+    sicc = SPAPR_INTC_GET_CLASS(new_intc);
+    if (sicc->activate) {
+        sicc->activate(new_intc, &error_fatal);
+    }
+
+    spapr->active_intc = new_intc;
+}
+
+void spapr_irq_update_active_intc(SpaprMachineState *spapr)
+{
+    SpaprInterruptController *new_intc;
+
+    if (!spapr->ics) {
+        /*
+         * XXX before we run CAS, ov5_cas is initialized empty, which
+         * indicates XICS, even if we have ic-mode=xive.  TODO: clean
+         * up the CAS path so that we have a clearer way of handling
+         * this.
+         */
+        new_intc = SPAPR_INTC(spapr->xive);
+    } else if (spapr_ovec_test(spapr->ov5_cas, OV5_XIVE_EXPLOIT)) {
+        new_intc = SPAPR_INTC(spapr->xive);
+    } else {
+        new_intc = SPAPR_INTC(spapr->ics);
+    }
+
+    set_active_intc(spapr, new_intc);
+}
+
 /*
  * XICS legacy routines - to deprecate one day
  */

include/hw/ppc/spapr.h

@@ -144,7 +144,6 @@ struct SpaprMachineState {
     struct SpaprVioBus *vio_bus;
     QLIST_HEAD(, SpaprPhbState) phbs;
     struct SpaprNvram *nvram;
-    ICSState *ics;
     SpaprRtcState rtc;
 
     SpaprResizeHpt resize_hpt;
@@ -196,9 +195,11 @@ struct SpaprMachineState {
 
     int32_t irq_map_nr;
     unsigned long *irq_map;
-    SpaprXive  *xive;
     SpaprIrq *irq;
     qemu_irq *qirqs;
+    SpaprInterruptController *active_intc;
+    ICSState *ics;
+    SpaprXive *xive;
 
     bool cmd_line_caps[SPAPR_CAP_NUM];
     SpaprCapabilities def, eff, mig;

include/hw/ppc/spapr_irq.h

@@ -44,6 +44,9 @@ typedef struct SpaprInterruptController SpaprInterruptController;
 typedef struct SpaprInterruptControllerClass {
     InterfaceClass parent;
 
+    int (*activate)(SpaprInterruptController *intc, Error **errp);
+    void (*deactivate)(SpaprInterruptController *intc);
+
     /*
      * These methods will typically be called on all intcs, active and
      * inactive
@@ -55,6 +58,8 @@ typedef struct SpaprInterruptControllerClass {
     void (*free_irq)(SpaprInterruptController *intc, int irq);
 } SpaprInterruptControllerClass;
 
+void spapr_irq_update_active_intc(SpaprMachineState *spapr);
+
 int spapr_irq_cpu_intc_create(SpaprMachineState *spapr,
                               PowerPCCPU *cpu, Error **errp);