linux-kernel - [PATCH] ACPI: do not mark TSC unstable for invalid C-states

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Date:	Mon, 11 May 2009 16:22:16 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Frans Pop <elendil@...net.nl>
cc:	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	len.brown@...el.com, mingo@...e.hu, johnstul@...ibm.com
Subject: [PATCH] ACPI: do not mark TSC unstable for invalid C-states

commit a71e4917dc0ebbcb5a0ecb7ca3486643c1c9a6e2 (ACPI: idle:
mark_tsc_unstable() at init-time, not run-time) marks TSC unstable
even on non affected systems.

The reason is that the state enumeration does not check the cx->valid
flag before calling tsc_halts_in_c(), so it marks TSC unstable for any
enumerated albeit invalid C state which is known to turn off TSC.

Check cx->valid before checking whether the TSC might become unstable.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 drivers/acpi/processor_idle.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/drivers/acpi/processor_idle.c
===================================================================
--- linux-2.6.orig/drivers/acpi/processor_idle.c
+++ linux-2.6/drivers/acpi/processor_idle.c
@@ -583,7 +583,7 @@ static int acpi_processor_power_verify(s
 
 #if defined (CONFIG_GENERIC_TIME) && defined (CONFIG_X86)
 		/* TSC could halt in idle, so notify users */
-		if (tsc_halts_in_c(cx->type))
+		if (cx->valid && tsc_halts_in_c(cx->type))
 			mark_tsc_unstable("TSC halts in idle");;
 #endif
 		switch (cx->type) {


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