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 <tglx@linutronix.de>
Signed-off-by: Daniel Drake <drake@endlessm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: len.brown@intel.com
Cc: linux@endlessm.com
Cc: rafael.j.wysocki@intel.com
Link: http://lkml.kernel.org/r/20190509055417.13152-1-drake@endlessm.com
Link: https://lkml.kernel.org/r/20190419083533.32388-1-drake@endlessm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 file changed
