irqchip/apple-aic: Fix irq_disable from within irq handlers

When disable_irq_nosync for an interrupt is called from within its
interrupt handler, this interrupt is only marked as disabled with the
intention to mask it when it triggers again.
The AIC hardware however automatically masks the interrupt when it is read.
aic_irq_eoi then unmasks it again if it's not disabled *and* not masked.
This results in a state mismatch between the hardware state and the
state kept in irq_data: The hardware interrupt is masked but
IRQD_IRQ_MASKED is not set. Any further calls to unmask_irq will directly
return and the interrupt can never be enabled again.

Fix this by keeping the hardware and irq_data state in sync by unmasking in
aic_irq_eoi if and only if the irq_data state also assumes the interrupt to
be unmasked.

Fixes: 76cde26394 ("irqchip/apple-aic: Add support for the Apple Interrupt Controller")
Signed-off-by: Sven Peter <sven@svenpeter.dev>
Acked-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210812100942.17206-1-sven@svenpeter.dev

drivers/irqchip/irq-apple-aic.c

@@ -226,7 +226,7 @@ static void aic_irq_eoi(struct irq_data *d)
 	 * Reading the interrupt reason automatically acknowledges and masks
 	 * the IRQ, so we just unmask it here if needed.
 	 */
-	if (!irqd_irq_disabled(d) && !irqd_irq_masked(d))
+	if (!irqd_irq_masked(d))
 		aic_irq_unmask(d);
 }