cpuidle/powerpc: Fix smt_snooze_delay functionality.

smt_snooze_delay was designed to delay idle loop's nap entry
in the native idle code before it got ported over to use as part of
the cpuidle framework.

A -ve value assigned to smt_snooze_delay should result in
busy looping, in other words disabling the entry to nap state.

- https://lists.ozlabs.org/pipermail/linuxppc-dev/2010-May/082450.html

This particular functionality can be achieved currently by
echo 1 > /sys/devices/system/cpu/cpu*/state1/disable
but it is broken when one assigns -ve value to the smt_snooze_delay
variable either via sysfs entry or ppc64_cpu util.

This patch aims to fix this, by disabling nap state when smt_snooze_delay
variable is set to -ve value.

Signed-off-by: Deepthi Dharwar <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/include/asm/processor.h

···
 extern void power7_nap(void);
 
 #ifdef CONFIG_PSERIES_IDLE
-extern void update_smt_snooze_delay(int snooze);
+extern void update_smt_snooze_delay(int cpu, int residency);
 #else
-static inline void update_smt_snooze_delay(int snooze) {}
+static inline void update_smt_snooze_delay(int cpu, int residency) {}
 #endif
 
 extern void flush_instruction_cache(void);

arch/powerpc/kernel/sysfs.c

···
 		return -EINVAL;
 
 	per_cpu(smt_snooze_delay, cpu->dev.id) = snooze;
-	update_smt_snooze_delay(snooze);
+	update_smt_snooze_delay(cpu->dev.id, snooze);
 
 	return count;
 }

arch/powerpc/platforms/pseries/processor_idle.c

···
 static struct cpuidle_device __percpu *pseries_cpuidle_devices;
 static struct cpuidle_state *cpuidle_state_table;
 
-void update_smt_snooze_delay(int snooze)
-{
-	struct cpuidle_driver *drv = cpuidle_get_driver();
-	if (drv)
-		drv->states[0].target_residency = snooze;
-}
-
 static inline void idle_loop_prolog(unsigned long *in_purr, ktime_t *kt_before)
 {
 
···
 		.target_residency = 0,
 		.enter = &shared_cede_loop },
 };
+
+void update_smt_snooze_delay(int cpu, int residency)
+{
+	struct cpuidle_driver *drv = cpuidle_get_driver();
+	struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);
+
+	if (cpuidle_state_table != dedicated_states)
+		return;
+
+	if (residency < 0) {
+		/* Disable the Nap state on that cpu */
+		if (dev)
+			dev->states_usage[1].disable = 1;
+	} else
+		if (drv)
+			drv->states[0].target_residency = residency;
+}
 
 static int pseries_cpuidle_add_cpu_notifier(struct notifier_block *n,
 			unsigned long action, void *hcpu)