[RFC PATCH 5/5] cpuidle/ppc: Add longnap state to the idle states on powernv

[Preeti U Murthy <preeti@linux.vnet.ibm.com>]

This patch hooks into the existing broadcast framework with the support that this
patchset introduces for ppc, and the cpuidle driver backend
for powernv(posted out recently by Deepthi Dharwar) to add sleep state as
one of the deep idle states, in which the decrementer is switched off.

However in this patch, we only emulate sleep by going into a state which does
a nap with the decrementer interrupts disabled, termed as longnap. This enables
focus on the timer broadcast framework for ppc in this series of patches ,
which is required as a first step to enable sleep on ppc.

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
---

 arch/powerpc/platforms/powernv/processor_idle.c |   48 +++++++++++++++++++++++
 1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/powernv/processor_idle.c b/arch/powerpc/platforms/powernv/processor_idle.c
index f43ad91a..9aca502 100644
--- a/arch/powerpc/platforms/powernv/processor_idle.c
+++ b/arch/powerpc/platforms/powernv/processor_idle.c
@@ -9,16 +9,18 @@
 #include <linux/cpuidle.h>
 #include <linux/cpu.h>
 #include <linux/notifier.h>
+#include <linux/clockchips.h>
 
 #include <asm/machdep.h>
 #include <asm/runlatch.h>
+#include <asm/time.h>
 
 struct cpuidle_driver powernv_idle_driver = {
 	.name =		"powernv_idle",
 	.owner =	THIS_MODULE,
 };
 
-#define MAX_IDLE_STATE_COUNT	2
+#define MAX_IDLE_STATE_COUNT	3
 
 static int max_idle_state = MAX_IDLE_STATE_COUNT - 1;
 static struct cpuidle_device __percpu *powernv_cpuidle_devices;
@@ -54,6 +56,43 @@ static int nap_loop(struct cpuidle_device *dev,
 	return index;
 }
 
+/* Emulate sleep, with long nap.
+ * During sleep, the core does not receive decrementer interrupts.
+ * Emulate sleep using long nap with decrementers interrupts disabled.
+ * This is an initial prototype to test the timer offload framework for ppc.
+ * We will eventually introduce the sleep state once the timer offload framework
+ * for ppc is stable.
+ */
+static int longnap_loop(struct cpuidle_device *dev,
+				struct cpuidle_driver *drv,
+				int index)
+{
+	int cpu = dev->cpu;
+
+	unsigned long lpcr = mfspr(SPRN_LPCR);
+
+	lpcr &= ~(LPCR_MER | LPCR_PECE); /* lpcr[mer] must be 0 */
+
+	/* exit powersave upon external interrupt, but not decrementer
+	 * interrupt, Emulate sleep.
+	 */
+	lpcr |= LPCR_PECE0;
+
+	if (cpu != bc_cpu) {
+		mtspr(SPRN_LPCR, lpcr);
+		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
+		power7_nap();
+		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
+	} else {
+		/* Wakeup on a decrementer interrupt, Do a nap */
+		lpcr |= LPCR_PECE1;
+		mtspr(SPRN_LPCR, lpcr);
+		power7_nap();
+	}
+
+	return index;
+}
+
 /*
  * States for dedicated partition case.
  */
@@ -72,6 +111,13 @@ static struct cpuidle_state powernv_states[MAX_IDLE_STATE_COUNT] = {
 		.exit_latency = 10,
 		.target_residency = 100,
 		.enter = &nap_loop },
+	 { /* LongNap */
+		.name = "LongNap",
+		.desc = "LongNap",
+		.flags = CPUIDLE_FLAG_TIME_VALID,
+		.exit_latency = 10,
+		.target_residency = 100,
+		.enter = &longnap_loop },
 };
 
 static int powernv_cpuidle_add_cpu_notifier(struct notifier_block *n,