Re: [PATCH v5 3/6] genirq/PM: Introduce IRQCHIP_ENABLE_WAKEUP_ON_SUSPEND flag

Thomas Gleixner
2020-09-04T09:54:10Z

Doug,

On Thu, Sep 03 2020 at 16:19, Doug Anderson wrote:
> On Thu, Sep 3, 2020 at 5:57 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>> That pending interrupt will not prevent the machine from going into
>> suspend and if it's an edge interrupt then an unmask in
>> suspend_device_irq() won't help. Edge interrupts are not resent in
>> hardware. They are fire and forget from the POV of the device
>> hardware.
>
> Ah, interesting. I didn't think about this case exactly. I might
> have a fix for it anyway. At some point in time I was thinking that
> the world could be solved by relying on lazily-disabled interrupts and
> I wrote up a patch to make sure that they woke things up. If you're
> willing to check out our gerrit you can look at:
>
> https://crrev.com/c/2314693
>
> ...if not I can post it as a RFC for you.

I actually tried despite my usual aversion against web
interfaces. Aversion confirmed :)

You could have included the 5 lines of patch into your reply to spare me
the experience. :)

> I'm sure I've solved the problem in a completely incorrect and broken
> way, but hopefully the idea makes sense. In discussion we decided not
> to go this way because it looked like IRQ clients could request an IRQ
> with IRQ_DISABLE_UNLAZY and then that'd break us. :( ...but even so I
> think the patch is roughly right and would address your point #1.

Kinda :) But that's still incomplete because it does not handle the case
where the interrupt arrives between disable_irq() and enable_irq_wake().
See below.

>> 2) irq chip has a irq_disable() callback or has IRQ_DISABLE_UNLAZY set
>>
>> In that case disable_irq() will mask it at the hardware level and it
>> stays that way until enable_irq() is invoked.
>>
>> #1 kinda works and the gap is reasonably trivial to fix in
>> suspend_device_irq() by checking the pending state and telling the PM
>> core that there is a wakeup pending.
>>
>> #2 Needs an indication from the chip flags that an interrupt which is
>> masked has to be unmasked when it is a enabled wakeup source.
>>
>> I assume your problem is #2, right? If it's #1 then UNMASK_IF_WAKEUP is
>> the wrong answer.
>
> Right, the problem is #2. We're not in the lazy mode.

Right and that's where we want the new chip flag with the unmask if
armed.

Thanks,

tglx

8<------

kernel/irq/pm.c | 27 ++++++++++++++++++++++-----
1 file changed, 22 insertions(+), 5 deletions(-)

--- a/kernel/irq/pm.c
+++ b/kernel/irq/pm.c
@@ -13,14 +13,19 @@

#include "internals.h"

+static void irq_pm_do_wakeup(struct irq_desc *desc)
+{
+ irqd_clear(&desc->irq_data, IRQD_WAKEUP_ARMED);
+ desc->istate |= IRQS_SUSPENDED | IRQS_PENDING;
+ pm_system_irq_wakeup(irq_desc_get_irq(desc));
+}
+
bool irq_pm_check_wakeup(struct irq_desc *desc)
{
if (irqd_is_wakeup_armed(&desc->irq_data)) {
- irqd_clear(&desc->irq_data, IRQD_WAKEUP_ARMED);
- desc->istate |= IRQS_SUSPENDED | IRQS_PENDING;
desc->depth++;
irq_disable(desc);
- pm_system_irq_wakeup(irq_desc_get_irq(desc));
+ irq_pm_do_wakeup(desc);
return true;
}
return false;
@@ -69,12 +74,24 @@ void irq_pm_remove_action(struct irq_des

static bool suspend_device_irq(struct irq_desc *desc)
{
+ struct irq_data *irqd = &desc->irq_data;
+
if (!desc->action || irq_desc_is_chained(desc) ||
desc->no_suspend_depth)
return false;

- if (irqd_is_wakeup_set(&desc->irq_data)) {
- irqd_set(&desc->irq_data, IRQD_WAKEUP_ARMED);
+ if (irqd_is_wakeup_set(irqd)) {
+ irqd_set(irqd, IRQD_WAKEUP_ARMED);
+ /*
+ * Interrupt might have been disabled in the suspend
+ * sequence before the wakeup was enabled. If the interrupt
+ * is lazy masked then it might have fired and the pending
+ * bit is set. Ignoring this would miss the wakeup.
+ */
+ if (irqd_irq_disabled(irqd) && desc->istate & IRQS_PENDING) {
+ irq_pm_do_wakeup(desc);
+ return false;
+ }
/*
* We return true here to force the caller to issue
* synchronize_irq(). We need to make sure that the