powerpc/powernv: Always go into nap mode when CPU is offline

The CPU hotplug code for the powernv platform currently only puts offline CPUs into nap mode if the powersave_nap variable is set. However, HV-style KVM on this platform requires secondary CPU threads to be offline and in nap mode. Since we know nap mode works just fine on all POWER7 machines, and the only machines that support the powernv platform are POWER7 machines, this changes the code to always put offline CPUs into nap mode, regardless of powersave_nap. Powersave_nap still controls whether or not CPUs go into nap mode when idle, as before. Signed-off-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Author: paulusmack

arch/powerpc/include/asm/processor.h

@@ -386,6 +386,7 @@ extern unsigned long cpuidle_disable;
 enum idle_boot_override {IDLE_NO_OVERRIDE = 0, IDLE_POWERSAVE_OFF};
 
 extern int powersave_nap;/* set if nap mode can be used in idle loop */
+extern void power7_nap(void);
 
 #ifdef CONFIG_PSERIES_IDLE
 extern void update_smt_snooze_delay(int snooze);

arch/powerpc/kernel/idle_power7.S

@@ -28,7 +28,9 @@ _GLOBAL(power7_idle)
 lwz	r4,ADDROFF(powersave_nap)(r3)
 cmpwi0,r4,0
 beqlr
+/* fall through */
 
+_GLOBAL(power7_nap)
 /* NAP is a state loss, we create a regs frame on the
  * stack, fill it up with the state we care about and
  * stick a pointer to it in PACAR1. We really only

arch/powerpc/platforms/powernv/smp.c

@@ -106,14 +106,6 @@ static void pnv_smp_cpu_kill_self(void)
 {
 unsigned int cpu;
 
-/* If powersave_nap is enabled, use NAP mode, else just
- * spin aimlessly
- */
-if (!powersave_nap) {
-generic_mach_cpu_die();
-return;
-}
-
 /* Standard hot unplug procedure */
 local_irq_disable();
 idle_task_exit();
@@ -128,7 +120,7 @@ static void pnv_smp_cpu_kill_self(void)
  */
 mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) & ~(u64)LPCR_PECE1);
 while (!generic_check_cpu_restart(cpu)) {
-power7_idle();
+power7_nap();
 if (!generic_check_cpu_restart(cpu)) {
 DBG("CPU%d Unexpected exit while offline !\n", cpu);
 /* We may be getting an IPI, so we re-enable