[PATCH] [18/20] x86: Don't disable TSC in any C states on AMD Fam10h

[Andi Kleen]

The ACPI code currently disables TSC use in any C2 and C3 
states. But the AMD Fam10h BKDG documents that the TSC
will never stop in any C states when the CONSTANT_TSC bit is 
set. Make this disabling conditional on CONSTANT_TSC
not set on AMD.

I actually think this is true on Intel too for C2 states
on CPUs with p-state invariant TSC, but this needs
further discussions with Len to really confirm :-) 

So far it is only enabled on AMD.

Cc: lenb@xxxxxxxxxx

Signed-off-by: Andi Kleen <ak@xxxxxxx>

---
 drivers/acpi/processor_idle.c |   32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

Index: linux/drivers/acpi/processor_idle.c
===================================================================
--- linux.orig/drivers/acpi/processor_idle.c
+++ linux/drivers/acpi/processor_idle.c
@@ -353,6 +353,26 @@ int acpi_processor_resume(struct acpi_de
 	return 0;
 }
 
+#if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86_TSC)
+static int tsc_halts_in_c(int state)
+{
+	switch (boot_cpu_data.x86_vendor) {
+	case X86_VENDOR_AMD:
+		/*
+		 * AMD Fam10h TSC will tick in all
+		 * C/P/S0/S1 states when this bit is set.
+		 */
+		if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
+			return 0;
+		/*FALL THROUGH*/
+	case X86_VENDOR_INTEL:
+		/* Several cases known where TSC halts in C2 too */
+	default:
+		return state > ACPI_STATE_C1;
+	}
+}
+#endif
+
 #ifndef CONFIG_CPU_IDLE
 static void acpi_processor_idle(void)
 {
@@ -512,7 +532,8 @@ static void acpi_processor_idle(void)
 
 #if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86_TSC)
 		/* TSC halts in C2, so notify users */
-		mark_tsc_unstable("possible TSC halt in C2");
+		if (tsc_halts_in_c(ACPI_STATE_C2))
+			mark_tsc_unstable("possible TSC halt in C2");
 #endif
 		/* Compute time (ticks) that we were actually asleep */
 		sleep_ticks = ticks_elapsed(t1, t2);
@@ -576,7 +597,8 @@ static void acpi_processor_idle(void)
 
 #if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86_TSC)
 		/* TSC halts in C3, so notify users */
-		mark_tsc_unstable("TSC halts in C3");
+		if (tsc_halts_in_c(ACPI_STATE_C3))
+			mark_tsc_unstable("TSC halts in C3");
 #endif
 		/* Compute time (ticks) that we were actually asleep */
 		sleep_ticks = ticks_elapsed(t1, t2);
@@ -1441,7 +1463,8 @@ static int acpi_idle_enter_simple(struct
 
 #if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86_TSC)
 	/* TSC could halt in idle, so notify users */
-	mark_tsc_unstable("TSC halts in idle");;
+	if (tsc_halts_in_c(cx->type))
+		mark_tsc_unstable("TSC halts in idle");;
 #endif
 	sleep_ticks = ticks_elapsed(t1, t2);
 
@@ -1552,7 +1575,8 @@ static int acpi_idle_enter_bm(struct cpu
 
 #if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86_TSC)
 	/* TSC could halt in idle, so notify users */
-	mark_tsc_unstable("TSC halts in idle");
+	if (tsc_halts_in_c(ACPI_STATE_C3))
+		mark_tsc_unstable("TSC halts in idle");
 #endif
 	sleep_ticks = ticks_elapsed(t1, t2);
 	/* Tell the scheduler how much we idled: */
--
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