• Thomas Gleixner's avatar
    x86: HPET: Chose a paranoid safe value for the ETIME check · f1c18071
    Thomas Gleixner authored
    commit 995bd3bb (x86: Hpet: Avoid the comparator readback penalty)
    chose 8 HPET cycles as a safe value for the ETIME check, as we had the
    confirmation that the posted write to the comparator register is
    delayed by two HPET clock cycles on Intel chipsets which showed
    readback problems.
    
    After that patch hit mainline we got reports from machines with newer
    AMD chipsets which seem to have an even longer delay. See
    http://thread.gmane.org/gmane.linux.kernel/1054283 and
    http://thread.gmane.org/gmane.linux.kernel/1069458 for further
    information.
    
    Boris tried to come up with an ACPI based selection of the minimum
    HPET cycles, but this failed on a couple of test machines. And of
    course we did not get any useful information from the hardware folks.
    
    For now our only option is to chose a paranoid high and safe value for
    the minimum HPET cycles used by the ETIME check. Adjust the minimum ns
    value for the HPET clockevent accordingly.
    Reported-Bistected-and-Tested-by: default avatarMarkus Trippelsdorf <markus@trippelsdorf.de>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    LKML-Reference: <alpine.LFD.2.00.1012131222420.2653@localhost6.localdomain6>
    Cc: Simon Kirby <sim@hostway.ca>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Andreas Herrmann <Andreas.Herrmann3@amd.com>
    Cc: John Stultz <johnstul@us.ibm.com>
    f1c18071
hpet.c 28.8 KB