ACPI x86: Make aperf/mperf MSR access in acpi_cpufreq read_only

Do not write zeroes to APERF and MPERF by ondemand governor. With this
change, other users can share these MSRs for reads.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c

@@ -68,6 +68,7 @@ struct acpi_cpufreq_data {
 	unsigned int max_freq;
 	unsigned int resume;
 	unsigned int cpu_feature;
+	u64 saved_aperf, saved_mperf;
 };
 
 static DEFINE_PER_CPU(struct acpi_cpufreq_data *, drv_data);
@@ -259,9 +260,6 @@ static long read_measured_perf_ctrs(void *_cur)
 	rdmsr(MSR_IA32_APERF, cur->aperf.split.lo, cur->aperf.split.hi);
 	rdmsr(MSR_IA32_MPERF, cur->mperf.split.lo, cur->mperf.split.hi);
 
-	wrmsr(MSR_IA32_APERF, 0, 0);
-	wrmsr(MSR_IA32_MPERF, 0, 0);
-
 	return 0;
 }
 
@@ -281,13 +279,20 @@ static long read_measured_perf_ctrs(void *_cur)
 static unsigned int get_measured_perf(struct cpufreq_policy *policy,
 				      unsigned int cpu)
 {
-	struct perf_pair cur;
+	struct perf_pair readin, cur;
 	unsigned int perf_percent;
 	unsigned int retval;
 
-	if (!work_on_cpu(cpu, read_measured_perf_ctrs, &cur))
+	if (!work_on_cpu(cpu, read_measured_perf_ctrs, &readin))
 		return 0;
 
+	cur.aperf.whole = readin.aperf.whole -
+				per_cpu(drv_data, cpu)->saved_aperf;
+	cur.mperf.whole = readin.mperf.whole -
+				per_cpu(drv_data, cpu)->saved_mperf;
+	per_cpu(drv_data, cpu)->saved_aperf = readin.aperf.whole;
+	per_cpu(drv_data, cpu)->saved_mperf = readin.mperf.whole;
+
 #ifdef __i386__
 	/*
 	 * We dont want to do 64 bit divide with 32 bit kernel