Eduardo Valentin [off-list ref] writes:
Hello Russell,
On Wed, Jan 05, 2011 at 06:19:18PM +0000, Russell King wrote:
quoted
On Wed, Jan 05, 2011 at 07:58:03PM +0200, Eduardo Valentin wrote:
quoted
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.
quoted
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
On Wed, Jan 05, 2011 at 03:22:51PM -0800, ext Kevin Hilman wrote:
Eduardo Valentin [off-list ref] writes:
quoted
Hello Russell,
On Wed, Jan 05, 2011 at 06:19:18PM +0000, Russell King wrote:
quoted
On Wed, Jan 05, 2011 at 07:58:03PM +0200, Eduardo Valentin wrote:
quoted
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.
Right. I'm convinced that the handler won't be called because of the lazy
disable mechanism.
quoted
quoted
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?
Yes I would want it.. of course, if the interrupt is enabled though..
I'm still trying to find a valid situation where someone disables an irq
but still wants its activity to be a wakeup source. I couldn't find so far..
If you don't want wakeups on that GPIO, then the driver should probably
be using disable_irq_wake().
Yes. Let's take this situation. Let's assume a driver, at its suspend callback,
explicitly reports to the system that its irq can be disabled and also should
not be seen as a wakeup source, by calling disable_irq(gpio_irq) and
disable_irq_wake(gpio_irq).
What should be the expected system behavior when the user says echo mem > /sys/power/state?