[PATCH v5 4/5] hpet 'driftfix': add code in update_irq() to detect coalesced interrupts (x86 apic only)

[Ulrich Obergfell <uobergfe@redhat.com>]

update_irq() uses a similar method as in 'rtc_td_hack' to detect
coalesced interrupts. The function entry addresses are retrieved
from 'target_get_irq_delivered' and 'target_reset_irq_delivered'.

This change can be replaced if a generic feedback infrastructure to
track coalesced IRQs for periodic, clock providing devices becomes
available.

Signed-off-by: Ulrich Obergfell <uobergfe@redhat.com>
---
 hw/hpet.c |   13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/hw/hpet.c b/hw/hpet.c
index dba9370..0428290 100644
--- a/hw/hpet.c
+++ b/hw/hpet.c
@@ -184,11 +184,12 @@ static inline uint64_t hpet_calculate_diff(HPETTimer *t, uint64_t current)
     }
 }
 
-static void update_irq(struct HPETTimer *timer, int set)
+static int update_irq(struct HPETTimer *timer, int set)
 {
     uint64_t mask;
     HPETState *s;
     int route;
+    int irq_delivered = 1;
 
     if (timer->tn <= 1 && hpet_in_legacy_mode(timer->state)) {
         /* if LegacyReplacementRoute bit is set, HPET specification requires
@@ -213,8 +214,16 @@ static void update_irq(struct HPETTimer *timer, int set)
         qemu_irq_raise(s->irqs[route]);
     } else {
         s->isr &= ~mask;
-        qemu_irq_pulse(s->irqs[route]);
+        if (s->driftfix) {
+            target_reset_irq_delivered();
+            qemu_irq_raise(s->irqs[route]);
+            irq_delivered = target_get_irq_delivered();
+            qemu_irq_lower(s->irqs[route]);
+        } else {
+            qemu_irq_pulse(s->irqs[route]);
+        }
     }
+    return irq_delivered;
 }
 
 static void hpet_pre_save(void *opaque)
-- 
1.6.2.5