[RFC V2 PATCH 4/6] 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 along with the support
that this patchset introduces for ppc, and the cpuidle driver backend
for powernv(posted out by Deepthi Dharwar:https://lkml.org/lkml/2013/7/23/128)
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,