Re: [Qemu-devel] [RFC PATCH v2 3/6] hw: arm_gic: Keep track of SGI sources

[Christoffer Dall <christoffer.dall@linaro.org>]

On Mon, Oct 14, 2013 at 05:33:38PM +0100, Peter Maydell wrote:
> On 14 October 2013 16:36, Peter Maydell <peter.maydell@linaro.org> wrote:

[...]

> 
> Tangentially, I notice that we don't correctly handle
> the PENDING bit for level triggered interrupts, since
> we do:
> 
>     /* Clear pending flags for both level and edge triggered interrupts.
>        Level triggered IRQs will be reasserted once they become inactive.  */
>     gic_clear_pending(s, new_irq, GIC_TEST_MODEL(new_irq) ? ALL_CPU_MASK : cm,
>                                   GIC_SGI_SRC(new_irq, cpu));
> 
> in gic_acknowledge_irq(). This is wrong, because section
> 3.2.4 is clear for a level triggered interrupt that if the
> interrupt signal remains asserted (which it usually will be)
> then we go from Pending to Active+Pending (whereas our
> current implementation goes from Pending to Active and
> then resets Pending later in gic_complete_irq()).
> 

Yes, I will send this patch to address this as part of the revised series:


diff --git a/hw/intc/arm_gic.c b/hw/intc/arm_gic.c
index bf1eb02..fce66c6 100644
--- a/hw/intc/arm_gic.c
+++ b/hw/intc/arm_gic.c
@@ -175,10 +180,15 @@ uint32_t gic_acknowledge_irq(GICState *s, int cpu)
         return 1023;
     }
     s->last_active[new_irq][cpu] = s->running_irq[cpu];
-    /* Clear pending flags for both level and edge triggered interrupts.
-       Level triggered IRQs will be reasserted once they become inactive.  */
-    gic_clear_pending(s, new_irq, GIC_TEST_MODEL(new_irq) ? ALL_CPU_MASK : cm,
-                                  GIC_SGI_SRC(new_irq, cpu));
+    /* Clear pending flags for edge-triggered and non-asserted level-triggered
+     * interrupts.
+     */
+    cm = GIC_TEST_MODEL(new_irq) ? ALL_CPU_MASK : cm;
+    if (GIC_TEST_TRIGGER(new_irq) || !GIC_TEST_LEVEL(new_irq, cm)) {
+        gic_clear_pending(s, new_irq, cm, GIC_SGI_SRC(new_irq, cpu));
+    }
+
     gic_set_running_irq(s, cpu, new_irq);
     DPRINTF("ACK %d\n", new_irq);
     return new_irq;

-- 
Christoffer