genirq: Work around __irq_set_handler vs stacked domains ordering issues

With the introduction of stacked domains, we have the issue that,
depending on where in the stack this is called, __irq_set_handler
will succeed or fail: If this is called from the inner irqchip,
__irq_set_handler() will fail, as it will look at the outer domain
as the (desc->irq_data.chip == &no_irq_chip) test fails (we haven't
set the top level yet).

This patch implements the following: "If there is at least one
valid irqchip in the domain, it will probably sort itself out".
This is clearly not ideal, but it is far less confusing then
crashing because the top-level domain is not up yet.

[ tglx: Added comment and a protection against chained interrupts in
  	that context ]

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Yingjoe Chen <yingjoe.chen@mediatek.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Link: http://lkml.kernel.org/r/1416048553-29289-3-git-send-email-marc.zyngier@arm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/irq/chip.c

@@ -731,7 +731,30 @@ __irq_set_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained,
 	if (!handle) {
 		handle = handle_bad_irq;
 	} else {
-		if (WARN_ON(desc->irq_data.chip == &no_irq_chip))
+		struct irq_data *irq_data = &desc->irq_data;
+#ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
+		/*
+		 * With hierarchical domains we might run into a
+		 * situation where the outermost chip is not yet set
+		 * up, but the inner chips are there.  Instead of
+		 * bailing we install the handler, but obviously we
+		 * cannot enable/startup the interrupt at this point.
+		 */
+		while (irq_data) {
+			if (irq_data->chip != &no_irq_chip)
+				break;
+			/*
+			 * Bail out if the outer chip is not set up
+			 * and the interrrupt supposed to be started
+			 * right away.
+			 */
+			if (WARN_ON(is_chained))
+				goto out;
+			/* Try the parent */
+			irq_data = irq_data->parent_data;
+		}
+#endif
+		if (WARN_ON(!irq_data || irq_data->chip == &no_irq_chip))
 			goto out;
 	}