Ensure that reads of the PMCCNTR_EL0 are monotonically increasing,
even for the smallest delta of two subsequent reads.
Signed-off-by: Christopher Covington <cov@xxxxxxxxxxxxxx>
---
arm/pmu.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/arm/pmu.c b/arm/pmu.c
index 91a3688..589e605 100644
--- a/arm/pmu.c
+++ b/arm/pmu.c
@@ -33,6 +33,8 @@ struct pmu_data {
};
};
+static const int samples = 10;
+
/* As a simple sanity check on the PMCR_EL0, ensure the implementer field isn't
* null. Also print out a couple other interesting fields for diagnostic
* purposes. For example, as of fall 2015, QEMU TCG mode doesn't implement
@@ -56,11 +58,38 @@ static bool check_pmcr(void)
return false;
}
+/* Ensure that the cycle counter progresses between back-to-back reads.
+ */
+static bool check_cycles_increase(void)
+{
+ struct pmu_data pmcr;
+
+ pmcr.enable = 1;
+ asm volatile("msr pmcr_el0, %0" : : "r" (pmcr));
+
+ for (int i = 0; i < samples; i++) {
+ int a, b;
+
+ asm volatile(
+ "mrs %[a], pmccntr_el0\n"
+ "mrs %[b], pmccntr_el0\n"
+ : [a] "=r" (a), [b] "=r" (b));
+
+ if (a >= b) {
+ printf("Read %d then %d.\n", a, b);
+ return false;
+ }
+ }
+
+ return true;
+}
+
int main(void)
{
report_prefix_push("pmu");
report("Control register", check_pmcr());
+ report("Monotonically increasing cycle count", check_cycles_increase());
return report_summary();
}
--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project
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