ARM: pm: add function to set WFI low-power mode for SMP CPUs

Add a function to set the SCU low-power mode for SMP CPUs.  This
centralizes this functionality rather than having to expose the
SCU register definitions to each platform.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/smp_scu.h

 #ifndef __ASMARM_ARCH_SCU_H
 #define __ASMARM_ARCH_SCU_H
 
+#define SCU_PM_NORMAL	0
+#define SCU_PM_DORMANT	2
+#define SCU_PM_POWEROFF	3
+
+#ifndef __ASSEMBLER__
 unsigned int scu_get_core_count(void __iomem *);
 void scu_enable(void __iomem *);
+int scu_power_mode(void __iomem *, unsigned int);
+#endif
 
 #endif

arch/arm/kernel/smp_scu.c

@@ -50,3 +50,26 @@ void __init scu_enable(void __iomem *scu_base)
 	 */
 	flush_cache_all();
 }
+
+/*
+ * Set the executing CPUs power mode as defined.  This will be in
+ * preparation for it executing a WFI instruction.
+ *
+ * This function must be called with preemption disabled, and as it
+ * has the side effect of disabling coherency, caches must have been
+ * flushed.  Interrupts must also have been disabled.
+ */
+int scu_power_mode(void __iomem *scu_base, unsigned int mode)
+{
+	unsigned int val;
+	int cpu = smp_processor_id();
+
+	if (mode > 3 || mode == 1 || cpu > 3)
+		return -EINVAL;
+
+	val = __raw_readb(scu_base + SCU_CPU_STATUS + cpu) & ~0x03;
+	val |= mode;
+	__raw_writeb(val, scu_base + SCU_CPU_STATUS + cpu);
+
+	return 0;
+}