On Mon, Oct 26, 2015 at 11:38:49AM -0400, Christopher Covington wrote:
> 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} };
One set of {} is enough, and looks better.
> +
> + 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
>
>
Otherwise
Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
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