Re: [RFC PATCH V2 09/11] xen: Clear IRQD_IRQ_STARTED flag during shutdown PIRQs

[Thomas Gleixner]

Anchal Agarwal <anchalag@xxxxxxxxxx> writes:
> On Wed, Jan 08, 2020 at 04:23:25PM +0100, Thomas Gleixner wrote:
>> Anchal Agarwal <anchalag@xxxxxxxxxx> writes:
>> > +void irq_state_clr_started(struct irq_desc *desc)
>> >  {
>> >  	irqd_clear(&desc->irq_data, IRQD_IRQ_STARTED);
>> >  }
>> > +EXPORT_SYMBOL_GPL(irq_state_clr_started);
>> 
>> This is core internal state and not supposed to be fiddled with by
>> drivers.
>> 
>> irq_chip has irq_suspend/resume/pm_shutdown callbacks for a reason.
>>
> I agree, as its mentioned in the previous patch {[RFC PATCH V2 08/11]} this is 
> one way of explicitly shutting down legacy devices without introducing too much 
> code for each of the legacy devices. . for eg. in case of floppy there 
> is no suspend/freeze handler which should have done the needful.
> .
> Either we implement them for all the legacy devices that have them missing or
> explicitly shutdown pirqs. I have choosen later for simplicity. I understand
> that ideally we should enable/disable devices interrupts in suspend/resume 
> devices but that requires adding code for doing that to few drivers[and I may
> not know all of them either]
>
> Now I discovered during the flow in hibernation_platform_enter under resume 
> devices that for such devices irq_startup is called which checks for 
> IRQD_IRQ_STARTED flag and based on that it calls irq_enable or irq_startup.
> They are only restarted if the flag is not set which is cleared during shutdown. 
> shutdown_pirq does not do that. Only masking/unmasking of evtchn does not work 
> as pirq needs to be restarted.
> xen-pirq.enable_irq is called rather than stratup_pirq. On resume if these pirqs
> are not restarted in this case ACPI SCI interrupts, I do not see receiving 
> any interrupts under cat /proc/interrupts even though host keeps generating 
> S4 ACPI events. 
> Does that makes sense?

No. You still violate all abstraction boundaries. On one hand you use a
XEN specific suspend function to shut down interrupts, but then you want
the core code to reestablish them on resume. That's just bad hackery which
abuses partial knowledge of core internals. The state flag is only one
part of the core internal state and just clearing it does not make the
rest consistent. It just works by chance and not by design and any
change of the core code will break it in colourful ways.

So either you can handle it purely on the XEN side without touching any
core state or you need to come up with some way of letting the core code
know that it should invoke shutdown instead of disable.

Something like the completely untested patch below.

Thanks,

       tglx

8<----------------

diff --git a/include/linux/irq.h b/include/linux/irq.h
index 7853eb9301f2..50f2057bc339 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -511,6 +511,7 @@ struct irq_chip {
  * IRQCHIP_EOI_THREADED:	Chip requires eoi() on unmask in threaded mode
  * IRQCHIP_SUPPORTS_LEVEL_MSI	Chip can provide two doorbells for Level MSIs
  * IRQCHIP_SUPPORTS_NMI:	Chip can deliver NMIs, only for root irqchips
+ * IRQCHIP_SHUTDOWN_ON_SUSPEND:	Shutdown non wake irqs in the suspend path
  */
 enum {
 	IRQCHIP_SET_TYPE_MASKED		= (1 <<  0),
@@ -522,6 +523,7 @@ enum {
 	IRQCHIP_EOI_THREADED		= (1 <<  6),
 	IRQCHIP_SUPPORTS_LEVEL_MSI	= (1 <<  7),
 	IRQCHIP_SUPPORTS_NMI		= (1 <<  8),
+	IRQCHIP_SHUTDOWN_ON_SUSPEND	= (1 <<  9),
 };
 
 #include <linux/irqdesc.h>
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index b3fa2d87d2f3..0fe355f72a15 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -233,7 +233,7 @@ __irq_startup_managed(struct irq_desc *desc, struct cpumask *aff, bool force)
 }
 #endif
 
-static int __irq_startup(struct irq_desc *desc)
+int __irq_startup(struct irq_desc *desc)
 {
 	struct irq_data *d = irq_desc_get_irq_data(desc);
 	int ret = 0;
diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
index 3924fbe829d4..11c7c55bda63 100644
--- a/kernel/irq/internals.h
+++ b/kernel/irq/internals.h
@@ -80,6 +80,7 @@ extern void __enable_irq(struct irq_desc *desc);
 extern int irq_activate(struct irq_desc *desc);
 extern int irq_activate_and_startup(struct irq_desc *desc, bool resend);
 extern int irq_startup(struct irq_desc *desc, bool resend, bool force);
+extern int __irq_startup(struct irq_desc *desc);
 
 extern void irq_shutdown(struct irq_desc *desc);
 extern void irq_shutdown_and_deactivate(struct irq_desc *desc);
diff --git a/kernel/irq/pm.c b/kernel/irq/pm.c
index 8f557fa1f4fe..597f0602510a 100644
--- a/kernel/irq/pm.c
+++ b/kernel/irq/pm.c
@@ -85,16 +85,22 @@ static bool suspend_device_irq(struct irq_desc *desc)
 	}
 
 	desc->istate |= IRQS_SUSPENDED;
-	__disable_irq(desc);
-
-	/*
-	 * Hardware which has no wakeup source configuration facility
-	 * requires that the non wakeup interrupts are masked at the
-	 * chip level. The chip implementation indicates that with
-	 * IRQCHIP_MASK_ON_SUSPEND.
-	 */
-	if (irq_desc_get_chip(desc)->flags & IRQCHIP_MASK_ON_SUSPEND)
-		mask_irq(desc);
+
+	/* Some irq chips (e.g. XEN PIRQ) require a full shutdown on suspend */
+	if (irq_desc_get_chip(desc)->flags & IRQCHIP_SHUTDOWN_ON_SUSPEND) {
+		irq_shutdown(desc);
+	} else {
+		__disable_irq(desc);
+
+		/*
+		 * Hardware which has no wakeup source configuration facility
+		 * requires that the non wakeup interrupts are masked at the
+		 * chip level. The chip implementation indicates that with
+		 * IRQCHIP_MASK_ON_SUSPEND.
+		 */
+		if (irq_desc_get_chip(desc)->flags & IRQCHIP_MASK_ON_SUSPEND)
+			mask_irq(desc);
+	}
 	return true;
 }
 
@@ -152,7 +158,10 @@ static void resume_irq(struct irq_desc *desc)
 	irq_state_set_masked(desc);
 resume:
 	desc->istate &= ~IRQS_SUSPENDED;
-	__enable_irq(desc);
+	if (irq_desc_get_chip(desc)->flags & IRQCHIP_SHUTDOWN_ON_SUSPEND)
+		__irq_startup(desc);
+	else
+		__enable_irq(desc);
 }
 
 static void resume_irqs(bool want_early)