[PATCH 1/1] arm: omap: gpio: define .disable callback for gpio irq chip

[Kevin Hilman]

Eduardo Valentin <eduardo.valentin at nokia.com> writes:

> Hello Russell,
>
> On Wed, Jan 05, 2011 at 06:19:18PM +0000, Russell King wrote:
>> On Wed, Jan 05, 2011 at 07:58:03PM +0200, Eduardo Valentin wrote:
>> > Currently, if one calls disable_irq(gpio_irq), the irq
>> > won't get disabled.
>> > 
>> > This is happening because the omap gpio code defines only
>> > a .mask callback. And the default_disable function is just
>> > a stub. The result is that, when someone calls disable_irq
>> > for an irq in a gpio line, it will be kept enabled.
>> > 
>> > This patch solves this issue by setting the .disable
>> > callback to point to the same .mask callback.
>> 
>> Amd this is a problem because?
>
> errr.. because the interrupt is enabled when it was supposed to be disabled?
>

As Russell pointed out, it's not actually "supposed" to be.

With lazy disable, what disable_irq() does is prevent the *handler* from
ever being called.  If another interrupt arrives, it will be caught by
the genirq core, marked as IRQ_PENDING and then masked.  This "don't
disable unless we really have to" is the desired behavior of the lazy
disable feature.

>> 
>> The way this works is that although it isn't disabled at that point,
>> if it never triggers, then everything remains happy.  However, if it
>> does trigger, the genirq code will then mask the interrupt and won't
>> call the handler.
>
> Right.. I didn't see from this point. I will check how that gets unmasked.
> But even so, if I understood correctly what you described, it would still
> open a time window which the system would see at least 1 interrupt during
> the time it was not suppose to. And that can wakeup a system which  is in
> deep sleep mode, either via dynamic idle or static suspend.
>
> It is unlikely, I know. But it can still happen. And can be avoided.

If the GPIO is configured as a wakeup source, then wouldn't you want
activity on that GPIO to wake up the system?

If you don't want wakeups on that GPIO, then the driver should probably
be using disable_irq_wake().

Kevin