[RFC PATCH V1 4/7] cpuidle: (powerpc) Add cpu_idle_wait() to allow switching idle routines

[Trinabh Gupta <trinabh@linux.vnet.ibm.com>]

This patch provides cpu_idle_wait() routine required
by the cpuidle subsystem. Almost all the code is borrowed
from x86.

Signed-off-by: Trinabh Gupta <trinabh@linux.vnet.ibm.com>
Signed-off-by: Arun R Bharadwaj <arun@linux.vnet.ibm.com>
---

 arch/powerpc/Kconfig              |    4 ++++
 arch/powerpc/include/asm/system.h |    1 +
 arch/powerpc/kernel/idle.c        |   18 ++++++++++++++++++
 3 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 2729c66..518beda 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -87,6 +87,10 @@ config ARCH_HAS_ILOG2_U64
 	bool
 	default y if 64BIT
 
+config ARCH_HAS_CPU_IDLE_WAIT
+	bool
+	default y
+
 config GENERIC_HWEIGHT
 	bool
 	default y
diff --git a/arch/powerpc/include/asm/system.h b/arch/powerpc/include/asm/system.h
index 2dc595d..811cdf1 100644
--- a/arch/powerpc/include/asm/system.h
+++ b/arch/powerpc/include/asm/system.h
@@ -222,6 +222,7 @@ extern unsigned long klimit;
 extern void *zalloc_maybe_bootmem(size_t size, gfp_t mask);
 
 extern int powersave_nap;	/* set if nap mode can be used in idle loop */
+void cpu_idle_wait(void);
 
 /*
  * Atomic exchange
diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
index 39a2baa..932392b 100644
--- a/arch/powerpc/kernel/idle.c
+++ b/arch/powerpc/kernel/idle.c
@@ -102,6 +102,24 @@ void cpu_idle(void)
 	}
 }
 
+static void do_nothing(void *unused)
+{
+}
+
+/*
+ * cpu_idle_wait - Used to ensure that all the CPUs come out of the old
+ * idle loop and start using the new idle loop.
+ * Required while changing idle handler on SMP systems.
+ * Caller must have changed idle handler to the new value before the call.
+ */
+void cpu_idle_wait(void)
+{
+	smp_mb();
+	/* kick all the CPUs so that they exit out of old idle routine */
+	smp_call_function(do_nothing, NULL, 1);
+}
+EXPORT_SYMBOL_GPL(cpu_idle_wait);
+
 int powersave_nap;
 
 #ifdef CONFIG_SYSCTL