[PATCH v3 2/2] perf/imx_ddr: don't enable counter0 if none of 4 counters

[Frank Li]

> -----Original Message-----
> From: Xu Yang <xu.yang_2 at nxp.com>
> Sent: Tuesday, August 8, 2023 2:28 AM
> To: Frank Li <frank.li at nxp.com>
> Cc: will at kernel.org; mark.rutland at arm.com; shawnguo at kernel.org;
> s.hauer at pengutronix.de; kernel at pengutronix.de; dl-linux-imx <linux-
> imx at nxp.com>; linux-arm-kernel at lists.infradead.org
> Subject: [PATCH v3 2/2] perf/imx_ddr: don't enable counter0 if none of 4
> counters
> 
> In current driver, counter0 will be enabled after ddr_perf_pmu_enable()
> is called even though none of the 4 counters are used. This will cause
> counter0 continue to count until ddr_perf_pmu_disabled() is called. If
> pmu is not disabled all the time, the pmu interrupt will be asserted
> from time to time due to counter0 will overflow and irq handler will
> clear it. It's not an expected behavior. This patch will not enable
> counter0 if none of 4 counters are used.
> 
> Fixes: 9a66d36cc7ac ("drivers/perf: imx_ddr: Add DDR performance counter
> support to perf")
> Signed-off-by: Xu Yang <xu.yang_2 at nxp.com>
> 
> ---
> Changes in v3:
>  - don't differentiate cycle counter and other counters
>  - modify logic in pmu_enable()/pmu_disable()
> Changes in v2:
>  - add active events count as suggested from Frank
> ---
>  drivers/perf/fsl_imx8_ddr_perf.c | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/perf/fsl_imx8_ddr_perf.c
> b/drivers/perf/fsl_imx8_ddr_perf.c
> index f8a94c051f41..32deeace2c93 100644
> --- a/drivers/perf/fsl_imx8_ddr_perf.c
> +++ b/drivers/perf/fsl_imx8_ddr_perf.c
> @@ -103,6 +103,7 @@ struct ddr_pmu {
>  	const struct fsl_ddr_devtype_data *devtype_data;
>  	int irq;
>  	int id;
> +	int active_count;
>  };
> 
>  static ssize_t ddr_perf_identifier_show(struct device *dev,
> @@ -516,6 +517,7 @@ static void ddr_perf_event_start(struct perf_event
> *event, int flags)
> 
>  	ddr_perf_counter_enable(pmu, event->attr.config, counter, true);
> 
> +	pmu->active_count++;
>  	hwc->state = 0;
>  }
> 
> @@ -569,6 +571,7 @@ static void ddr_perf_event_stop(struct perf_event
> *event, int flags)
>  	ddr_perf_counter_enable(pmu, event->attr.config, counter, false);
>  	ddr_perf_event_update(event);
> 
> +	pmu->active_count--;
>  	hwc->state |= PERF_HES_STOPPED;
>  }
> 
> @@ -588,8 +591,11 @@ static void ddr_perf_pmu_enable(struct pmu *pmu)
>  {
>  	struct ddr_pmu *ddr_pmu = to_ddr_pmu(pmu);
> 
> -	/* enable cycle counter if cycle is not active event list */
> -	if (ddr_pmu->events[EVENT_CYCLES_COUNTER] == NULL)
> +	/*
> +	 * Because counter 1-3 depend on cycle counter, treat cycle
> +	 * counter as main switch when any counter of the 4 need to run.
> +	 */
> +	if (ddr_pmu->active_count > 0)
>  		ddr_perf_counter_enable(ddr_pmu,
>  				      EVENT_CYCLES_ID,
>  				      EVENT_CYCLES_COUNTER,
> @@ -600,11 +606,13 @@ static void ddr_perf_pmu_disable(struct pmu
> *pmu)
>  {
>  	struct ddr_pmu *ddr_pmu = to_ddr_pmu(pmu);
> 
> -	if (ddr_pmu->events[EVENT_CYCLES_COUNTER] == NULL)
> -		ddr_perf_counter_enable(ddr_pmu,
> -				      EVENT_CYCLES_ID,
> -				      EVENT_CYCLES_COUNTER,
> -				      false);
> +	/*
> +	 * Counting should be stopped. Disable cycle counter unconditionally.
> +	 */
> +	ddr_perf_counter_enable(ddr_pmu,
> +			      EVENT_CYCLES_ID,
> +			      EVENT_CYCLES_COUNTER,
> +			      false);

What's happen if one event is running in back ground,  but another event try
to disable it.

>  }
> 
>  static int ddr_perf_init(struct ddr_pmu *pmu, void __iomem *base,
> --
> 2.34.1