Re: [Xen-devel] [PATCH-4.5 4/4] xen/arm: set GICH_HCR_NPIE if all the LRs are in use

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 07/02/14 18:56, Stefano Stabellini wrote:
> On return to guest, if there are no free LRs and we still have more
> interrupt to inject, set GICH_HCR_NPIE so that we are going to receive a
> maintenance interrupt when no pending interrupts are present in the LR
> registers.
> The maintenance interrupt handler won't do anything anymore, but
> receiving the interrupt is going to cause gic_inject to be called on
> return to guest that is going to clear the old LRs and inject new
> interrupts.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> ---
>   xen/arch/arm/gic.c |    8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
> index 87bd5d3..bee2618 100644
> --- a/xen/arch/arm/gic.c
> +++ b/xen/arch/arm/gic.c
> @@ -810,8 +810,14 @@ void gic_inject(void)
>       gic_restore_pending_irqs(current);
>       if (!gic_events_need_delivery())
>           gic_inject_irq_stop();
> -    else
> +    else {
>           gic_inject_irq_start();
> +    }
> +
> +    if ( !list_empty(&current->arch.vgic.lr_pending) )
> +        GICH[GICH_HCR] = GICH_HCR_EN | GICH_HCR_NPIE;
> +    else
> +        GICH[GICH_HCR] = GICH_HCR_EN;
Any reason to not move this in the else?

BTW, I think we can safely avoid to reinject the IRQ for the event 
channels if there is pending events. It will also avoid spurious IRQ on 
some specific case :).
--
Julien Grall

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