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    Subject[v1 7/9] x86/tsc: use cpuid to determine CPU frequency
    Date
    Newer processors implement cpuid extension to determine CPU frequency
    from cpuid. This patch adds a function that can do this early in boot.

    Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
    ---
    arch/x86/kernel/tsc.c | 10 ++++++----
    1 files changed, 6 insertions(+), 4 deletions(-)

    diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
    index 1c9fc23..58bd575 100644
    --- a/arch/x86/kernel/tsc.c
    +++ b/arch/x86/kernel/tsc.c
    @@ -743,14 +743,14 @@ unsigned long native_calibrate_tsc(void)
    return tsc_khz;
    }

    -static unsigned long cpu_khz_from_cpuid(void)
    +static unsigned long cpu_khz_from_cpuid_early(int vendor, int cpuid_level)
    {
    unsigned int eax_base_mhz, ebx_max_mhz, ecx_bus_mhz, edx;

    - if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
    + if (vendor != X86_VENDOR_INTEL)
    return 0;

    - if (boot_cpu_data.cpuid_level < 0x16)
    + if (cpuid_level < 0x16)
    return 0;

    eax_base_mhz = ebx_max_mhz = ecx_bus_mhz = edx = 0;
    @@ -770,7 +770,9 @@ unsigned long native_calibrate_cpu(void)
    unsigned long flags, latch, ms, fast_calibrate;
    int hpet = is_hpet_enabled(), i, loopmin;

    - fast_calibrate = cpu_khz_from_cpuid();
    + fast_calibrate = cpu_khz_from_cpuid_early(boot_cpu_data.x86_vendor,
    + boot_cpu_data.cpuid_level);
    +
    if (fast_calibrate)
    return fast_calibrate;

    --
    1.7.1
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