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Re: [Qemu-devel] [RFC PATCH v3 01/10] hw: arm_gic: Fix gic_set_irq handl


From: Peter Maydell
Subject: Re: [Qemu-devel] [RFC PATCH v3 01/10] hw: arm_gic: Fix gic_set_irq handling
Date: Thu, 28 Nov 2013 16:17:43 +0000

On 19 November 2013 06:18, Christoffer Dall <address@hidden> wrote:
> For some reason only edge-triggered or enabled level-triggered
> interrupts would set the pending state of a raised IRQ.  This is not in
> compliance with the specs, which indicate that the pending state is
> separate from the enabled state, which only controls if a pending
> interrupt is actually forwarded to the CPU interface.
>
> Therefore, simply always set the pending state on a rising edge, but
> only clear the pending state of falling edge if the interrupt is level
> triggered.
>
> Changelog [v2]:
>  - Fix bisection issue, by not using gic_clear_pending yet.
>
> Signed-off-by: Christoffer Dall <address@hidden>
> ---
>  hw/intc/arm_gic.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/hw/intc/arm_gic.c b/hw/intc/arm_gic.c
> index d431b7a..c7a24d5 100644
> --- a/hw/intc/arm_gic.c
> +++ b/hw/intc/arm_gic.c
> @@ -128,11 +128,12 @@ static void gic_set_irq(void *opaque, int irq, int 
> level)
>
>      if (level) {
>          GIC_SET_LEVEL(irq, cm);
> -        if (GIC_TEST_TRIGGER(irq) || GIC_TEST_ENABLED(irq, cm)) {
> -            DPRINTF("Set %d pending mask %x\n", irq, target);
> -            GIC_SET_PENDING(irq, target);
> -        }
> +        DPRINTF("Set %d pending mask %x\n", irq, target);
> +        GIC_SET_PENDING(irq, target);
>      } else {
> +        if (!GIC_TEST_TRIGGER(irq)) {
> +            GIC_CLEAR_PENDING(irq, target);
> +        }
>          GIC_CLEAR_LEVEL(irq, cm);
>      }
>      gic_update(s);

So I think this is a correct change in the sense that
it's fixing the behaviour of this function. However
we seem to get our pending behaviour for level triggered
interrupts wrong in several places:
 * here
 * gic_acknowledge_irq (which you fix in a later patch)
 * gic_complete_irq, which currently says "enabled
   level triggered still-raised interrupts should be
   remarked as pending"

This feels to me like a cluster of errors which have come
from somebody's misreading of the spec and which probably
combine to produce a coherent not-too-far-from-correct
result, and which we should therefore fix all at once rather
than only partially.

thanks
-- PMM



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