[Qemu-devel] [PATCH KVM v2 4/4] KVM: i8259: refactor pic_set_irq level logic

[Matthew Ogilvie <mmogilvi_qemu@miniinfo.net>]

No change in functionality.

Clarify that the only difference between level triggered and
edge triggered interrupts is on the leading edge.

Signed-off-by: Matthew Ogilvie <mmogilvi_qemu@miniinfo.net>
---
 arch/x86/kvm/i8259.c | 28 +++++++++++-----------------
 1 file changed, 11 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
index 76d8dc1..63f731b 100644
--- a/arch/x86/kvm/i8259.c
+++ b/arch/x86/kvm/i8259.c
@@ -95,26 +95,20 @@ static inline int pic_set_irq1(struct kvm_kpic_state *s, int irq, int level)
 {
 	int mask, ret = 1;
 	mask = 1 << irq;
-	if (s->elcr & mask)	/* level triggered */
-		if (level) {
+	if (level) {
+		if ((s->last_irr & mask) == 0 ||  /* edge for edge-triggered */
+		    (s->elcr & mask)) {           /* or level triggered */
 			ret = !(s->irr & mask);
 			s->irr |= mask;
-			s->last_irr |= mask;
-		} else {
-			s->irr &= ~mask;
-			s->last_irr &= ~mask;
-		}
-	else	/* edge triggered */
-		if (level) {
-			if ((s->last_irr & mask) == 0) {
-				ret = !(s->irr & mask);
-				s->irr |= mask;
-			}
-			s->last_irr |= mask;
-		} else {
-			s->irr &= ~mask;
-			s->last_irr &= ~mask;
 		}
+		s->last_irr |= mask;
+	} else {
+		/* Dropping level clears the interrupt regardless of edge
+		 * trigger vs level trigger.
+		 */
+		s->irr &= ~mask;
+		s->last_irr &= ~mask;
+	}
 
 	return (s->imr & mask) ? -1 : ret;
 }
-- 
1.7.10.2.484.gcd07cc5