[PATCH v5 01/11] arm-cci: Define CCI counter period

Mark Rutland
2016-01-04T18:27:52Z

On Mon, Jan 04, 2016 at 11:54:40AM +0000, Suzuki K. Poulose wrote:
> Instead of hard coding the period we program on the PMU
> counters, define a symbol.
>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Punit Agrawal <punit.agrawal@arm.com>
> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@arm.com>
> ---
> drivers/bus/arm-cci.c | 19 ++++++++++---------
> 1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c
> index ee47e6b..3786879 100644
> --- a/drivers/bus/arm-cci.c
> +++ b/drivers/bus/arm-cci.c
> @@ -85,6 +85,14 @@ static const struct of_device_id arm_cci_matches[] = {
> #define CCI_PMU_CNTR_MASK ((1ULL << 32) -1)
> #define CCI_PMU_CNTR_LAST(cci_pmu) (cci_pmu->num_cntrs - 1)
>
> +/*
> + * The CCI PMU counters have a period of 2^32. To account for the
> + * possiblity of extreme interrupt latency we program for a period of
> + * half that. Hopefully we can handle the interrupt before another 2^31
> + * events occur and the counter overtakes its previous value.
> + */
> +#define CCI_CNTR_PERIOD (1UL << 31)
> +
> #define CCI_PMU_MAX_HW_CNTRS(model) \
> ((model)->num_hw_cntrs + (model)->fixed_hw_cntrs)
>
> @@ -797,15 +805,8 @@ static void pmu_read(struct perf_event *event)
> void pmu_event_set_period(struct perf_event *event)
> {
> struct hw_perf_event *hwc = &event->hw;
> - /*
> - * The CCI PMU counters have a period of 2^32. To account for the
> - * possiblity of extreme interrupt latency we program for a period of
> - * half that. Hopefully we can handle the interrupt before another 2^31
> - * events occur and the counter overtakes its previous value.
> - */
> - u64 val = 1ULL << 31;
> - local64_set(&hwc->prev_count, val);
> - pmu_write_counter(event, val);
> + local64_set(&hwc->prev_count, CCI_CNTR_PERIOD);
> + pmu_write_counter(event, CCI_CNTR_PERIOD);

I think this is a little misleading (and confusing), as we're conflating
the period with its inverse. This wouldn't work for any other value of
CCI_CNTR_PERIOD.

Perhaps s/PERIOD/START_VAL/, leaving everything else as-is?

Thanks,
Mark.