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authorAndi Kleen <ak@suse.de>2006-02-03 23:51:41 +0300
committerLinus Torvalds <torvalds@g5.osdl.org>2006-02-05 03:43:15 +0300
commit0c3749c41f5eee0da36bbf92b2793338b4d8574f (patch)
tree3af004c5533ab04297004f5ec40da4c6801b8fda /Documentation/x86_64
parent099f318b8d97490e58c595eb1b6d3415da5ccc03 (diff)
downloadlinux-0c3749c41f5eee0da36bbf92b2793338b4d8574f.tar.xz
[PATCH] x86_64: Calibrate APIC timer using PM timer
On some broken motherboards (at least one NForce3 based AMD64 laptop) the PIT timer runs at a incorrect frequency. This patch adds a new option "apicpmtimer" that allows to use the APIC timer and calibrate it using the PMTimer. It requires the earlier patch that allows to run the main timer from the APIC. Specifying apicpmtimer implies apicmaintimer. The option defaults to off for now. I tested it on a few systems and the resulting APIC timer frequencies were usually a bit off, but always <1%, which should be tolerable. TBD figure out heuristic to enable this automatically on the affected systems TBD perhaps do it on all NForce3s or using DMI? Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation/x86_64')
-rw-r--r--Documentation/x86_64/boot-options.txt5
1 files changed, 5 insertions, 0 deletions
diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index 654ea4fccff8..153740f460a6 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -47,6 +47,11 @@ APICs
noapicmaintimer Don't do time keeping using the APIC timer.
Useful when this option was auto selected, but doesn't work.
+ apicpmtimer
+ Do APIC timer calibration using the pmtimer. Implies
+ apicmaintimer. Useful when your PIT timer is totally
+ broken.
+
Early Console
syntax: earlyprintk=vga