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x86/tsc: Mark Intel ATOM_GOLDMONT TSC reliable

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On Intel GOLDMONT Atom SoC TSC is the only available clocksource, so there
is no way to do software calibration or have a watchdog clocksource for it.
Software calibration is already disabled via the TSC_KNOWN_FREQ flag, but
the watchdog requirement still persists, so such systems cannot switch to
high resolution/nohz mode.

Mark it reliable, so it becomes usable. Hardware teams confirmed that this
is safe on that SoC.

Signed-off-by: Bin Gao <bin.gao@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1479241644-234277-4-git-send-email-bin.gao@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Bin Gao 2016-11-15 12:27:23 -08:00 committed by Thomas Gleixner
parent 4ca4df0b7e
commit 4635fdc696
1 changed files with 7 additions and 0 deletions
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7
arch/x86/kernel/tsc.c
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@ -709,6 +709,13 @@ unsigned long native_calibrate_tsc(void)
*/
setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
/*
* For Atom SoCs TSC is the only reliable clocksource.
* Mark TSC reliable so no watchdog on it.
*/
if (boot_cpu_data.x86_model == INTEL_FAM6_ATOM_GOLDMONT)
setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
return crystal_khz * ebx_numerator / eax_denominator;
}