irqchip/gic-v2, v3: Implement irq_chip->irq_retrigger()

While digging around IRQCHIP_EOI_IF_HANDLED and irq/resend.c, it has come
to my attention that the IRQ resend situation seems a bit precarious for
the GIC(s).

When marking an IRQ with IRQS_PENDING, handle_fasteoi_irq() will bail out
and issue an irq_eoi(). Should the IRQ in question be re-enabled,
check_irq_resend() will trigger a SW resend, which will go through the flow
handler again and issue *another* irq_eoi() on the *same* IRQ
activation. This is something the GIC spec clearly describes as a bad idea:
any EOI must match a previous ACK.

Implement irq_chip.irq_retrigger() for the GIC chips by setting the GIC
pending bit of the relevant IRQ. After being called by check_irq_resend(),
this will eventually trigger a *new* interrupt which we will handle as usual.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200730170321.31228-2-valentin.schneider@arm.com

drivers/irqchip/irq-gic-v3.c

@@ -1207,6 +1207,11 @@ static int gic_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
 #define gic_smp_init()		do { } while(0)
 #endif
 
+static int gic_retrigger(struct irq_data *data)
+{
+	return !gic_irq_set_irqchip_state(data, IRQCHIP_STATE_PENDING, true);
+}
+
 #ifdef CONFIG_CPU_PM
 static int gic_cpu_pm_notifier(struct notifier_block *self,
 			       unsigned long cmd, void *v)
@@ -1242,6 +1247,7 @@ static struct irq_chip gic_chip = {
 	.irq_eoi		= gic_eoi_irq,
 	.irq_set_type		= gic_set_type,
 	.irq_set_affinity	= gic_set_affinity,
+	.irq_retrigger          = gic_retrigger,
 	.irq_get_irqchip_state	= gic_irq_get_irqchip_state,
 	.irq_set_irqchip_state	= gic_irq_set_irqchip_state,
 	.irq_nmi_setup		= gic_irq_nmi_setup,
@@ -1258,6 +1264,7 @@ static struct irq_chip gic_eoimode1_chip = {
 	.irq_eoi		= gic_eoimode1_eoi_irq,
 	.irq_set_type		= gic_set_type,
 	.irq_set_affinity	= gic_set_affinity,
+	.irq_retrigger          = gic_retrigger,
 	.irq_get_irqchip_state	= gic_irq_get_irqchip_state,
 	.irq_set_irqchip_state	= gic_irq_set_irqchip_state,
 	.irq_set_vcpu_affinity	= gic_irq_set_vcpu_affinity,

drivers/irqchip/irq-gic.c

@@ -347,6 +347,11 @@ static int gic_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
 }
 #endif
 
+static int gic_retrigger(struct irq_data *data)
+{
+	return !gic_irq_set_irqchip_state(data, IRQCHIP_STATE_PENDING, true);
+}
+
 static void __exception_irq_entry gic_handle_irq(struct pt_regs *regs)
 {
 	u32 irqstat, irqnr;
@@ -417,6 +422,7 @@ static const struct irq_chip gic_chip = {
 	.irq_unmask		= gic_unmask_irq,
 	.irq_eoi		= gic_eoi_irq,
 	.irq_set_type		= gic_set_type,
+	.irq_retrigger          = gic_retrigger,
 	.irq_get_irqchip_state	= gic_irq_get_irqchip_state,
 	.irq_set_irqchip_state	= gic_irq_set_irqchip_state,
 	.flags			= IRQCHIP_SET_TYPE_MASKED |