powerpc/powernv: Enable POWER8 doorbell IPIs

This patch enables POWER8 doorbell IPIs on powernv.

Since doorbells can only IPI within a core, we test to see when we can use
doorbells and if not we fall back to XICS.  This also enables hypervisor
doorbells to wakeup us up from nap/sleep via the LPCR PECEDH bit.

Based on tests by Anton, the best case IPI latency between two threads dropped
from 894ns to 512ns.
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/cpu_setup_power.S

@@ -56,6 +56,7 @@ _GLOBAL(__setup_cpu_power8)
 	li	r0,0
 	mtspr	SPRN_LPID,r0
 	mfspr	r3,SPRN_LPCR
+	ori	r3, r3, LPCR_PECEDH
 	bl	__init_LPCR
 	bl	__init_HFSCR
 	bl	__init_tlb_power8
@@ -74,6 +75,7 @@ _GLOBAL(__restore_cpu_power8)
 	li	r0,0
 	mtspr	SPRN_LPID,r0
 	mfspr   r3,SPRN_LPCR
+	ori	r3, r3, LPCR_PECEDH
 	bl	__init_LPCR
 	bl	__init_HFSCR
 	bl	__init_tlb_power8

arch/powerpc/platforms/powernv/Kconfig

@@ -17,6 +17,7 @@ config PPC_POWERNV
 	select CPU_FREQ_GOV_USERSPACE
 	select CPU_FREQ_GOV_ONDEMAND
 	select CPU_FREQ_GOV_CONSERVATIVE
+	select PPC_DOORBELL
 	default y
 
 config PPC_POWERNV_RTAS

arch/powerpc/platforms/powernv/smp.c

@@ -32,6 +32,7 @@
 #include <asm/opal.h>
 #include <asm/runlatch.h>
 #include <asm/code-patching.h>
+#include <asm/dbell.h>
 
 #include "powernv.h"
 
@@ -46,6 +47,11 @@ static void pnv_smp_setup_cpu(int cpu)
 {
 	if (cpu != boot_cpuid)
 		xics_setup_cpu();
+
+#ifdef CONFIG_PPC_DOORBELL
+	if (cpu_has_feature(CPU_FTR_DBELL))
+		doorbell_setup_this_cpu();
+#endif
 }
 
 int pnv_smp_kick_cpu(int nr)

arch/powerpc/platforms/pseries/Kconfig

@@ -21,6 +21,7 @@ config PPC_PSERIES
 	select HAVE_CONTEXT_TRACKING
 	select HOTPLUG_CPU if SMP
 	select ARCH_RANDOM
+	select PPC_DOORBELL
 	default y
 
 config PPC_SPLPAR

arch/powerpc/sysdev/xics/icp-native.c

@@ -26,6 +26,7 @@
 #include <asm/errno.h>
 #include <asm/xics.h>
 #include <asm/kvm_ppc.h>
+#include <asm/dbell.h>
 
 struct icp_ipl {
 	union {
@@ -145,6 +146,12 @@ static unsigned int icp_native_get_irq(void)
 static void icp_native_cause_ipi(int cpu, unsigned long data)
 {
 	kvmppc_set_host_ipi(cpu, 1);
+#ifdef CONFIG_PPC_DOORBELL
+	if (cpu_has_feature(CPU_FTR_DBELL) &&
+	    (cpumask_test_cpu(cpu, cpu_sibling_mask(smp_processor_id()))))
+		doorbell_cause_ipi(cpu, data);
+	else
+#endif
 		icp_native_set_qirr(cpu, IPI_PRIORITY);
 }