From 44fee88cea43d3c2cac962e0439cb10a3cabff6d Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 13 Mar 2017 15:57:12 +0100 Subject: [PATCH] x86/tsc: Fix ART for TSC_KNOWN_FREQ Subhransu reported that convert_art_to_tsc() isn't working for him. The ART to TSC relation is only set up for systems which use the refined TSC calibration. Systems with known TSC frequency (available via CPUID 15) are not using the refined calibration and therefor the ART to TSC relation is never established. Add the setup to the known frequency init path which skips ART calibration. The init code needs to be duplicated as for systems which use refined calibration the ART setup must be delayed until calibration has been done. The problem has been there since the ART support was introdduced, but only detected now because Subhransu tested the first time on hardware which has TSC frequency enumerated via CPUID 15. Note for stable: The conditional has changed from TSC_RELIABLE to TSC_KNOWN_FREQUENCY. [ tglx: Rewrote changelog and identified the proper 'Fixes' commit ] Fixes: f9677e0f8308 ("x86/tsc: Always Running Timer (ART) correlated clocksource") Reported-by: "Prusty, Subhransu S" Signed-off-by: Peter Zijlstra (Intel) Cc: stable@vger.kernel.org Cc: christopher.s.hall@intel.com Cc: kevin.b.stanton@intel.com Cc: john.stultz@linaro.org Cc: akataria@vmware.com Link: http://lkml.kernel.org/r/20170313145712.GI3312@twins.programming.kicks-ass.net Signed-off-by: Thomas Gleixner --- arch/x86/kernel/tsc.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 4f7a9833d8e5..c73a7f9e881a 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -1333,6 +1333,8 @@ static int __init init_tsc_clocksource(void) * the refined calibration and directly register it as a clocksource. */ if (boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) { + if (boot_cpu_has(X86_FEATURE_ART)) + art_related_clocksource = &clocksource_tsc; clocksource_register_khz(&clocksource_tsc, tsc_khz); return 0; } -- 2.20.1