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>

2 files changed, 7 insertions, 0 deletions

diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
index c252ee95bddf..45a8ed0585cd 100644
--- a/arch/powerpc/platforms/powernv/Kconfig
+++ b/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
diff --git a/arch/powerpc/platforms/powernv/smp.c b/arch/powerpc/platforms/powernv/smp.c
index 0062a43a2e0d..5fcfcf44e3a9 100644
--- a/arch/powerpc/platforms/powernv/smp.c
+++ b/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)