From: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Date: Thu, 15 Oct 2015 19:34:21 +0000 (-0700)
Subject: cpufreq: intel_pstate: Fix divide by zero on Knights Landing (KNL)
X-Git-Tag: v4.2.6~8
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a7e19859f9fd6eb9e5a11e5645fe42082df40d8a;p=thirdparty%2Fkernel%2Fstable.git

cpufreq: intel_pstate: Fix divide by zero on Knights Landing (KNL)

commit 8e601a9f97a00bab031980de34f9a81891c1f82f upstream.

This is a workaround for KNL platform, where in some cases MPERF counter
will not have updated value before next read of MSR_IA32_MPERF. In this
case divide by zero will occur. This change ignores current sample for
busy calculation in this case.

Fixes: b34ef932d79a (intel_pstate: Knights Landing support)
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Acked-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index fcb929ec5304a..aba2117a80c12 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -766,6 +766,11 @@ static inline void intel_pstate_sample(struct cpudata *cpu)
 	local_irq_save(flags);
 	rdmsrl(MSR_IA32_APERF, aperf);
 	rdmsrl(MSR_IA32_MPERF, mperf);
+	if (cpu->prev_mperf == mperf) {
+		local_irq_restore(flags);
+		return;
+	}
+
 	tsc = native_read_tsc();
 	local_irq_restore(flags);