x86/tsc: Use CPUID.0x16 to calculate missing crystal frequency

native_calibrate_tsc() had a data mapping Intel CPU families
and crystal clock speed, but hardcoded tables are not ideal, and this
approach was already problematic at least in the Skylake X case, as
seen in commit:

  b51120309348 ("x86/tsc: Fix erroneous TSC rate on Skylake Xeon")

By examining CPUID data from http://instlatx64.atw.hu/ and units
in the lab, we have found that 3 different scenarios need to be dealt
with, and we can eliminate most of the hardcoded data using an approach a
little more advanced than before:

 1. ApolloLake, GeminiLake, CannonLake (and presumably all new chipsets
    from this point) report the crystal frequency directly via CPUID.0x15.
    That's definitive data that we can rely upon.

 2. 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.

 3. Denverton (GOLDMONT_X) reports a crystal frequency of zero and does
    not support CPUID.0x16, so we leave this entry hardcoded.

Suggested-by: Thomas Gleixner <[email protected]>
Signed-off-by: Daniel Drake <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions