genirq: irq_chip->startup() usage in setup_irq and set_irq_chained handler

This patch clarifies usage of irq_chip->startup() callback:

1. The "if (startup) startup(); else enabled();" code in setup_irq()
   is unnecessary, as startup() falls back to enabled() via
   default callbacks, set by irq_chip_set_defaults().

2. When using set_irq_chained_handler() the startup() was never called,
   which is not good at all... Fixed. And again - when startup() is not
   defined the call will fall back to enable() than to unmask() via
   default callbacks.
Signed-off-by: NPawel Moll <pawel.moll@st.com>
Acked-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/irq/chip.c

@@ -587,7 +587,7 @@ __set_irq_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained,
 		desc->status &= ~IRQ_DISABLED;
 		desc->status |= IRQ_NOREQUEST | IRQ_NOPROBE;
 		desc->depth = 0;
-		desc->chip->unmask(irq);
+		desc->chip->startup(irq);
 	}
 	spin_unlock_irqrestore(&desc->lock, flags);
 }

kernel/irq/manage.c

@@ -397,10 +397,7 @@ int setup_irq(unsigned int irq, struct irqaction *new)
 		if (!(desc->status & IRQ_NOAUTOEN)) {
 			desc->depth = 0;
 			desc->status &= ~IRQ_DISABLED;
-			if (desc->chip->startup)
-				desc->chip->startup(irq);
-			else
-				desc->chip->enable(irq);
+			desc->chip->startup(irq);
 		} else
 			/* Undo nested disables: */
 			desc->depth = 1;