[Bug 240475] [PATCH]: Add support for CPUID 0x16 in tsc_freq_cpuid() (TSC clock)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=240475

--- Comment #3 from Neel Chauhan <neel at neelc.org> ---
This patch is based upon an existing Linux commit:
https://github.com/torvalds/linux/commit/604dc9170f2435d27da5039a3efd757dceadc684

In the commit message:

    Skylake, Kabylake and all variants of those two chipsets report a
    crystal frequency of zero, however we can calculate the crystal clock
    speed by condidering data from CPUID.0x16.

    This method correctly distinguishes between the two crystal clock
    frequencies present on different Skylake X variants that caused
    headaches before.

    As the calculations do not quite match the previously-hardcoded values
    in some cases (e.g. 23913043Hz instead of 24MHz), TSC refinement is
    enabled on all platforms where we had to calculate the crystal
    frequency in this way.

This is also true on my system.

I will post two verbose dmesgs: one without any patches, and one with this
patch (which also has drm-kmod and Vladimir Kondratyev's iichid loaded).

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