linux-kernel - Re: [PATCH 1/2] x86: GEODE fix MFGPT input clock value

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Message-ID: <20080123221053.GA2455@1wt.eu>
Date:	Wed, 23 Jan 2008 23:10:53 +0100
From:	Willy Tarreau <w@....eu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Arnd Hannemann <hannemann@...informatik.rwth-aachen.de>,
	Jordan Crouse <jordan.crouse@....com>,
	Lars Heete <hel@...in.de>,
	Andres Salomon <dilinger@...ued.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/2] x86: GEODE fix MFGPT input clock value

On Wed, Jan 23, 2008 at 02:22:59PM -0800, H. Peter Anvin wrote:
> Willy Tarreau wrote:
> >Hi Peter,
> >
> >On Wed, Jan 23, 2008 at 01:59:32PM -0800, H. Peter Anvin wrote:
> >>Willy Tarreau wrote:
> >>>The GEODE MFGPT code assumed that 32kHz was 32000 Hz while the boards
> >>>run on a 32.768 kHz digital watch crystal. In practise, it will not
> >>>change the timer's frequency as the skew was only 2.4%, but it
> >>>should provide more accurate intervals.
> >>>- *  Divisor   Hz      Min Delta (S) Max Delta (S)
> >>Seconds are "s", not "S" (S = siemens.)
> >
> >You're quite right. Same as we should write kHz and not Khz. But I'm
> >used to change other people's work and particularly comments the least
> >possible. Do you want an update ?
> >
> 
> I much prefer to see this done right.  I have a pretty case-sensitive 
> brain, it seems.

Oh rest assured that you're not alone. I was smiling reading Andrew's
comments about people who "cnat tpye", and I must admit that I too am
often quite irritated by incorrect case and inverted letters, but I try
to refrain from whining, people say that I do it too much and for nothing :-)

OK, here it comes updated.

Willy


>From 3a314dd5c2a694f5b0a1c1b8b5690ee28f711b5e Mon Sep 17 00:00:00 2001
From: Willy Tarreau <w@....eu>
Date: Wed, 23 Jan 2008 23:05:50 +0100
Subject: [PATCH 1/2] x86: GEODE fix MFGPT input clock value

The GEODE MFGPT code assumed that 32kHz was 32000 Hz while the boards
run on a 32.768 kHz digital watch crystal. In practise, it will not
change the timer's frequency as the skew was only 2.4%, but it
should provide more accurate intervals.

Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/x86/kernel/mfgpt_32.c |   27 +++++++++++++--------------
 1 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/mfgpt_32.c b/arch/x86/kernel/mfgpt_32.c
index 3960ab7..f97e6e3 100644
--- a/arch/x86/kernel/mfgpt_32.c
+++ b/arch/x86/kernel/mfgpt_32.c
@@ -12,21 +12,20 @@
  */
 
 /*
- * We are using the 32Khz input clock - its the only one that has the
+ * We are using the 32.768kHz input clock - its the only one that has the
  * ranges we find desirable.  The following table lists the suitable
- * divisors and the associated hz, minimum interval
- * and the maximum interval:
+ * divisors and the associated Hz, minimum interval and the maximum interval:
  *
- *  Divisor   Hz      Min Delta (S) Max Delta (S)
- *   1        32000     .0005          2.048
- *   2        16000      .001          4.096
- *   4         8000      .002          8.192
- *   8         4000      .004         16.384
- *   16        2000      .008         32.768
- *   32        1000      .016         65.536
- *   64         500      .032        131.072
- *  128         250      .064        262.144
- *  256         125      .128        524.288
+ *  Divisor   Hz      Min Delta (s)  Max Delta (s)
+ *   1        32768   .00048828125      2.000
+ *   2        16384   .0009765625       4.000
+ *   4         8192   .001953125        8.000
+ *   8         4096   .00390625        16.000
+ *   16        2048   .0078125         32.000
+ *   32        1024   .015625          64.000
+ *   64         512   .03125          128.000
+ *  128         256   .0625           256.000
+ *  256         128   .125            512.000
  */
 
 #include <linux/kernel.h>
@@ -45,7 +44,7 @@ static struct mfgpt_timer_t {
 
 #define MFGPT_DIVISOR 16
 #define MFGPT_SCALE  4     /* divisor = 2^(scale) */
-#define MFGPT_HZ  (32000 / MFGPT_DIVISOR)
+#define MFGPT_HZ  (32768 / MFGPT_DIVISOR)
 #define MFGPT_PERIODIC (MFGPT_HZ / HZ)
 
 #ifdef CONFIG_GEODE_MFGPT_TIMER
-- 
1.5.3.3

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