linux-kernel - [PATCH] -rt fix TSC calibration from PM Timer

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Date:	Mon, 21 May 2007 17:43:09 +0200
From:	"Joachim Deguara" <joachim.deguara@....com>
To:	"LKML" <linux-kernel@...r.kernel.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>
Subject: [PATCH] -rt fix TSC calibration from PM Timer

The code to calibrate TSC frequency from the PM timer does not work on my 
laptop with the 2.6.21-rt5.

[    0.247815] time.c: Detected 62117.606 MHz processor.

The code looks to be copied from the calibration from HPET but unfortunately 
it reports frequency instead of period in femtoseconds as the HPET does.  I 
also rearranged the math to make the femtoseconds and kHz clearer but it does 
loose a negligible amount of precision.

Signed-off-by: Joachim Deguara <joachim.deguara@....com>

Index: 2.6-rt/arch/x86_64/kernel/tsc.c
===================================================================
--- 2.6-rt.orig/arch/x86_64/kernel/tsc.c
+++ 2.6-rt/arch/x86_64/kernel/tsc.c
@@ -187,14 +187,14 @@ void __init tsc_calibrate(void)
 		return;
 	}
 
-	tsc2 = (tsc2 - tsc1) * 1000000000L;
+	tsc2 = tsc2 - tsc1;
 
 	if (hpet) {
 		hpet2 = (hpet2 - hpet1) & 0xFFFFFFFF;
-		tsc1 = (hpet2 * hpet_readl(HPET_PERIOD)) / 1000;
+		tsc1 = hpet2 * hpet_readl(HPET_PERIOD) / 1e12;
 	} else {
 		pm2 = (pm2 -pm1) & ACPI_PM_MASK;
-		tsc1 = (pm2 * PMTMR_TICKS_PER_SEC) / 1000;
+		tsc1 = (pm2 * 1e3) / PMTMR_TICKS_PER_SEC;
 	}
 
 	tsc_khz = tsc2 / tsc1;


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