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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 10 Feb 2014, Julien Grall wrote:
> On 02/10/2014 04:59 PM, Stefano Stabellini wrote:
> > On Fri, 7 Feb 2014, Julien Grall wrote:
> >> 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?
> > 
> > Yes: we need to be able to disable GICH_HCR_NPIE even if there are no
> > irqs to inject.
> 
> In this case, can we simply enable/disable GICH_HCR_NPIE instead of
> resetting the register every time? GICH_HCR contains other bits that
> could be set in the future.

Sure

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