powerpc/microwatt: Define an idle power-save function

This uses the 'wait' instruction to pause instruction execution when
idle until an interrupt occurs.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/Z5xtl1m_Gqc-HLjY@thinks.paulus.ozlabs.org

arch/powerpc/platforms/microwatt/setup.c

@@ -34,10 +34,19 @@ static void __init microwatt_setup_arch(void)
 	microwatt_rng_init();
 }
 
+static void microwatt_idle(void)
+{
+	if (!prep_irq_for_idle_irqsoff())
+		return;
+
+	__asm__ __volatile__ ("wait");
+}
+
 define_machine(microwatt) {
 	.name			= "microwatt",
 	.compatible		= "microwatt-soc",
 	.init_IRQ		= microwatt_init_IRQ,
 	.setup_arch		= microwatt_setup_arch,
 	.progress		= udbg_progress,
+	.power_save		= microwatt_idle,
 };