• Andi Kleen's avatar
    [PATCH] x86_64: Calibrate APIC timer using PM timer · 0c3749c4
    Andi Kleen authored
    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: default avatarAndi Kleen <ak@suse.de>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    0c3749c4
pmtimer.c 2.75 KB