i386/145718: [PATCH] fix freq calculation from MSR for CPUs with fractional multipliers

[Andre Albsmeier]

>Number:         145718
>Category:       i386
>Synopsis:       [PATCH] fix freq calculation from MSR for CPUs with fractional multipliers
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-i386
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Apr 15 08:40:00 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator:     Andre Albsmeier
>Release:        FreeBSD 7.3-STABLE i386
>Organization:
>Environment:

System: FreeBSD 7.3-STABLE #6: Thu Apr 15 09:42:06 CEST 2010

using a Q9550 cpu

>Description:

When calculating the simple rate table in est_msr_info()
we have to observe bit 6 (0x40) of the multiplier which
denotes an additional 0.5 for the value. Examples:

FID	Multiplier
--------------------
0x06	6
0x07	7
0x08	8
0x46	6.5
0x47	7.5
0x48	8.5

>How-To-Repeat:

Enable cpufreq on a cpu with a fractional multiplier (in
my case a Q9550 which uses 8.5), set hw.est.msr_info=1,
and watch dmesg spitting out insane low/high values for
the bus clock.

>Fix:

--- est.c.ORI	2009-07-14 08:57:29.000000000 +0200
+++ est.c	2010-04-15 10:29:11.000000000 +0200
@@ -1207,11 +1207,15 @@
 	freq = tsc_freq / 1000000;
 	id = msr >> 32;
 	bus = freq / (id >> 8);
+	if( id & 0x4000 )
+	  bus = 2 * freq / ( (id >> 7 & 0x7e) + 1 );
 	device_printf(dev, "Guessed bus clock (high) of %d MHz\n", bus);
 	if (!bus_speed_ok(bus)) {
 		/* We may be running on the low frequency. */
 		id = msr >> 48;
 		bus = freq / (id >> 8);
+		if( id & 0x4000 )
+		  bus = 2 * freq / ( (id >> 7 & 0x7e) + 1 );
 		device_printf(dev, "Guessed bus clock (low) of %d MHz\n", bus);
 		if (!bus_speed_ok(bus))
 			return (EOPNOTSUPP);
@@ -1219,6 +1223,8 @@
 		/* Calculate high frequency. */
 		id = msr >> 32;
 		freq = ((id >> 8) & 0xff) * bus;
+		if( id & 0x4000 )
+		  freq =( (id >> 7 & 0x7e) + 1 ) * bus / 2;
 	}
 
 	/* Fill out a new freq table containing just the high and low freqs. */
@@ -1241,6 +1247,8 @@
 	/* Second, the low frequency. */
 	id = msr >> 48;
 	freq = ((id >> 8) & 0xff) * bus;
+	if( id & 0x4000 )
+	  freq =( (id >> 7 & 0x7e) + 1 ) * bus / 2;
 	volts = id & 0xff;
 	if (volts != 0) {
 		volts <<= 4;
>Release-Note:
>Audit-Trail:
>Unformatted: