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 | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 60 insertions(+)
diff --git a/arm/pmu.c b/arm/pmu.c
index 42d0ee1..c44d708 100644
--- a/arm/pmu.c
+++ b/arm/pmu.c
@@ -14,6 +14,8 @@
*/
#include "libcflat.h"
+#define NR_SAMPLES 10
+
#if defined(__arm__)
static inline uint32_t get_pmcr(void)
{
@@ -22,6 +24,25 @@ static inline uint32_t get_pmcr(void)
asm volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (ret));
return ret;
}
+
+static inline void set_pmcr(uint32_t pmcr)
+{
+ asm volatile("mcr p15, 0, %0, c9, c12, 0" : : "r" (pmcr));
+}
+
+/*
+ * While PMCCNTR can be accessed as a 64 bit coprocessor register, returning 64
+ * bits doesn't seem worth the trouble when differential usage of the result is
+ * expected (with differences that can easily fit in 32 bits). So just return
+ * the lower 32 bits of the cycle count in AArch32.
+ */
+static inline unsigned long get_pmccntr(void)
+{
+ unsigned long cycles;
+
+ asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r" (cycles));
+ return cycles;
+}
#elif defined(__aarch64__)
static inline uint32_t get_pmcr(void)
{
@@ -30,6 +51,19 @@ static inline uint32_t get_pmcr(void)
asm volatile("mrs %0, pmcr_el0" : "=r" (ret));
return ret;
}
+
+static inline void set_pmcr(uint32_t pmcr)
+{
+ asm volatile("msr pmcr_el0, %0" : : "r" (pmcr));
+}
+
+static inline unsigned long get_pmccntr(void)
+{
+ unsigned long cycles;
+
+ asm volatile("mrs %0, pmccntr_el0" : "=r" (cycles));
+ return cycles;
+}
#endif
struct pmu_data {
@@ -72,11 +106,37 @@ static bool check_pmcr(void)
return pmu.implementer != 0;
}
+/*
+ * Ensure that the cycle counter progresses between back-to-back reads.
+ */
+static bool check_cycles_increase(void)
+{
+ struct pmu_data pmu = { {0} };
+
+ pmu.enable = 1;
+ set_pmcr(pmu.pmcr_el0);
+
+ for (int i = 0; i < NR_SAMPLES; i++) {
+ unsigned long a, b;
+
+ a = get_pmccntr();
+ b = get_pmccntr();
+
+ if (a >= b) {
+ printf("Read %ld then %ld.\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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