MIPS: cevt-r4k: Make interrupt handler shared

Make the cevt-r4k interrupt handler shared so that other interrupt
handlers (specifically the performance counter overflow handler and fast
debug channel interrupt handler) can share the same interrupt line.

This simply imvolves returning IRQ_NONE when no timer interrupt has been
handled to allow other handlers to run, and passing IRQF_SHARED when
setting up the IRQ handler so that other handlers (with compatible
flags) can be registered.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/9128/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/cevt-r4k.c

@@ -80,6 +80,8 @@ irqreturn_t c0_compare_interrupt(int irq, void *dev_id)
 		write_c0_compare(read_c0_compare());
 		cd = &per_cpu(mips_clockevent_device, cpu);
 		cd->event_handler(cd);
+	} else {
+		return IRQ_NONE;
 	}
 
 out:
@@ -88,7 +90,11 @@ irqreturn_t c0_compare_interrupt(int irq, void *dev_id)
 
 struct irqaction c0_compare_irqaction = {
 	.handler = c0_compare_interrupt,
-	.flags = IRQF_PERCPU | IRQF_TIMER,
+	/*
+	 * IRQF_SHARED: The timer interrupt may be shared with other interrupts
+	 * such as perf counter and FDC interrupts.
+	 */
+	.flags = IRQF_PERCPU | IRQF_TIMER | IRQF_SHARED,
 	.name = "timer",
 };