linux-kernel - [PATCH] x86: add the X86_FEATURE_NONSTOP_TSC

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Message-ID: <87ppdik875.fsf@jcompost-MOBL1.tl.intel.com>
Date:	Thu, 23 Oct 2014 19:27:26 +0200
From:	jeremy.compostella@...el.com (Compostella, Jeremy)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org,
	"Kumar P\, Mahesh" <mahesh.kumar.p@...el.com>,
	"Afantenos\, Marie Cecile" <marie.cecile.afantenos@...el.com>,
	"Jeremy Compostell" <jeremy.compostella@...il.com>
Subject: [PATCH] x86: add the X86_FEATURE_NONSTOP_TSC_S3 cpu capability to new cpu

New Intel Atom processors (Baytrail and Cherryview), have a TSC that won't stop
in S3 state, say the TSC value won't be reset to 0 after resume.  This feature
makes TSC a more reliable clocksource and could benefit the timekeeping code
during system suspend/resume cycle.

Signed-off-by: Jeremy Compostella <jeremy.compostella@...el.com>
---
 arch/x86/kernel/cpu/intel.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 1ef4562..8af195e 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -92,11 +92,16 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 			set_sched_clock_stable();
 	}
 
-	/* Penwell and Cloverview have the TSC which doesn't sleep on S3 */
+	/*
+	 * Penwell, Cloverview, Valleyview and Cherryview have the TSC
+	 * which doesn't sleep on S3.
+	 */
 	if (c->x86 == 6) {
 		switch (c->x86_model) {
 		case 0x27:	/* Penwell */
 		case 0x35:	/* Cloverview */
+		case 0x37:	/* Valleyview */
+		case 0x4C:	/* Cherryview */
 			set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC_S3);
 			break;
 		default:
-- 
1.9.1

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