IRQCHIP_MASK_ON_SUSPEND and the gic

[Santosh Shilimkar]

Thomas,

On 7/14/2011 7:13 AM, Colin Cross wrote:
> Quick background:
> The gic is an interrupt controller commonly found in SMP ARM devices.
> It has no power management capabilities, and is turned off when the
> cpu is powered down in suspend.  In order to wake the device out of
> suspend, a second interrupt controller is placed in series with the
> gic, passing each interrupt through along with a mask.  If an unmasked
> interrupt is received at the secondary controller, and the cpu is
> powered down, a wakeup is triggered.
>
> In order to keep the cpu from waking on masked interrupts during
> cpuidle, the secondary controller masks must be updated at the same
> time as the gic masks.  This is handled through the gic_arch_extn
> irqchip pointer that is filled out by each architecture.
>
> During suspend, the same registers used by mask/unmask need to be
> programmed to have all wakeup interrupts unmasked, and all non-wakeup
> interrupts masked.  I believe the unmasking is already taken care of:
> every interrupt starts as unmasked, and is lazily masked only when an
> interrupt arrives while it is disabled.  When check_wakeup_irqs is
> called in suspend, every interrupt is guaranteed to be either
> unmasked, or masked and marked pending.  Pending wakeup irqs will
> abort suspend, so every wakeup interrupt is guaranteed to be unmasked
> after check_wakeup_irqs.
>
> That leaves masking, which can easily be handled by setting the
> IRQCHIP_MASK_ON_SUSPEND flag on the gic irqchip (propagated from the
> gic_arch_extn irqchip).
>
> So, finally, my question: there is nothing for each secondary
> interrupt controller driver to do in a set_wake handler, but if its
> not implemented, enable_irq_wake will return an error.  Is there any
> way to avoid implementing an empty set_wake handler?  Should the
> missing handler not be an error if IRQCHIP_MASK_ON_SUSPEND is set?

Any comments on this?
I guess some thing like below should remove a need of dummy
set_wake() handler for irq_chips with IRQCHIP_MASK_ON_SUSPEND set.

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 0a7840a..cd4bc01 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -467,6 +467,9 @@ static int set_irq_wake_real(unsigned int irq, 
unsigned int on)
  	struct irq_desc *desc = irq_to_desc(irq);
  	int ret = -ENXIO;

+	if (irq_desc_get_chip(desc)->flags & IRQCHIP_MASK_ON_SUSPEND)
+		return 0;
+
  	if (desc->irq_data.chip->irq_set_wake)
  		ret = desc->irq_data.chip->irq_set_wake(&desc->irq_data, on);

-- 
1.6.0.4

Regards
Santosh