irqchip/git-v3-its: Implement irq_retrigger callback for device-triggered LPIs

It is pretty easy to provide a retrigger callback for the ITS,
as it we already have the required support in terms of
irq_set_irqchip_state().

Note that this only works for device-generated LPIs, and not
the GICv4 doorbells, which should never have to be retriggered
anyway.
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

drivers/irqchip/irq-gic-v3-its.c

@@ -1720,6 +1720,11 @@ static int its_irq_set_irqchip_state(struct irq_data *d,
 	return 0;
 }
 
+static int its_irq_retrigger(struct irq_data *d)
+{
+	return !its_irq_set_irqchip_state(d, IRQCHIP_STATE_PENDING, true);
+}
+
 /*
  * Two favourable cases:
  *
@@ -1971,6 +1976,7 @@ static struct irq_chip its_irq_chip = {
 	.irq_set_affinity	= its_set_affinity,
 	.irq_compose_msi_msg	= its_irq_compose_msi_msg,
 	.irq_set_irqchip_state	= its_irq_set_irqchip_state,
+	.irq_retrigger		= its_irq_retrigger,
 	.irq_set_vcpu_affinity	= its_irq_set_vcpu_affinity,
 };