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

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

Doug,

On Thu, Sep 03 2020 at 16:19, Doug Anderson wrote:
> On Thu, Sep 3, 2020 at 5:57 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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