Subject: Re: [PATCH v4 06/21] PM / devfreq: rockchip-dfi: Use free running counter

From: Jonathan Cameron <[email-masked]>
Date: Tue, 16 May 2023 16:48:43 +0100

On Fri,  5 May 2023 13:38:41 +0200
Sascha Hauer <[email-masked]> wrote:

> The DDR_MON counters are free running counters. These are resetted to 0
> when starting them over like currently done when reading the current
> counter values.
> 
> Resetting the counters becomes a problem with perf support we want to
> add later, because perf needs a monotonicly increasing counter.

In general, perf doesn't, but it does need to know no one else is modifying it,
so I guess this makes sense.

> 
> This patch removes resetting the counters and keeps them running
> instead. Counter overflows are handled with modular arithmetics. Not
> stopping the counters also has the impact that they are running while
> we are reading them. We cannot read multiple timers atomically, so
> the values do not exactly fit together. The effect should be negligible
> though as the time between two measurements is some orders of magnitude
> bigger than the time we need to read multiple registers.
> 
> Signed-off-by: Sascha Hauer <[email-masked]>

> ---
>  drivers/devfreq/event/rockchip-dfi.c | 53 ++++++++++++++++------------
>  1 file changed, 31 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/devfreq/event/rockchip-dfi.c b/drivers/devfreq/event/rockchip-dfi.c
> index 383fe8a17a512..25d64d9166a9a 100644
> --- a/drivers/devfreq/event/rockchip-dfi.c
> +++ b/drivers/devfreq/event/rockchip-dfi.c
> @@ -38,11 +38,15 @@
>  #define DDRMON_CH1_COUNT_NUM		0x3c
>  #define DDRMON_CH1_DFI_ACCESS_NUM	0x40
>  
> -struct dmc_usage {
> +struct dmc_count_channel {
>  	u32 access;
>  	u32 total;
>  };
>  
> +struct dmc_count {
> +	struct dmc_count_channel c[RK3399_DMC_NUM_CH];
> +};
> +
>  /*
>   * The dfi controller can monitor DDR load. It has an upper and lower threshold
>   * for the operating points. Whenever the usage leaves these bounds an event is
> @@ -51,7 +55,8 @@ struct dmc_usage {
>  struct rockchip_dfi {
>  	struct devfreq_event_dev *edev;
>  	struct devfreq_event_desc desc;
> -	struct dmc_usage ch_usage[RK3399_DMC_NUM_CH];
> +	struct dmc_count count;

Is count used?  Looking at the code I'd guess you changed to a local variable at
some point and forgot to drop this.

> +	struct dmc_count last_event_count;
>  	struct device *dev;
>  	void __iomem *regs;
>  	struct regmap *regmap_pmu;
> @@ -85,30 +90,18 @@ static void rockchip_dfi_stop_hardware_counter(struct devfreq_event_dev *edev)
>  	writel_relaxed(SOFTWARE_DIS, dfi_regs + DDRMON_CTRL);
>  }
>  
> -static int rockchip_dfi_get_busier_ch(struct devfreq_event_dev *edev)
> +static void rockchip_dfi_read_counters(struct devfreq_event_dev *edev, struct dmc_count *count)
>  {
>  	struct rockchip_dfi *dfi = devfreq_event_get_drvdata(edev);
> -	u32 tmp, max = 0;
> -	u32 i, busier_ch = 0;
> +	u32 i;
>  	void __iomem *dfi_regs = dfi->regs;
>  
> -	rockchip_dfi_stop_hardware_counter(edev);
> -
> -	/* Find out which channel is busier */
>  	for (i = 0; i < RK3399_DMC_NUM_CH; i++) {
> -		dfi->ch_usage[i].access = readl_relaxed(dfi_regs +
> +		count->c[i].access = readl_relaxed(dfi_regs +
>  				DDRMON_CH0_DFI_ACCESS_NUM + i * 20);
> -		dfi->ch_usage[i].total = readl_relaxed(dfi_regs +
> +		count->c[i].total = readl_relaxed(dfi_regs +
>  				DDRMON_CH0_COUNT_NUM + i * 20);
> -		tmp = dfi->ch_usage[i].access;
> -		if (tmp > max) {
> -			busier_ch = i;
> -			max = tmp;
> -		}
>  	}
> -	rockchip_dfi_start_hardware_counter(edev);
> -
> -	return busier_ch;
>  }
>  
>  static int rockchip_dfi_disable(struct devfreq_event_dev *edev)
> @@ -145,12 +138,28 @@ static int rockchip_dfi_get_event(struct devfreq_event_dev *edev,
>  				  struct devfreq_event_data *edata)
>  {
>  	struct rockchip_dfi *dfi = devfreq_event_get_drvdata(edev);
> -	int busier_ch;
> +	struct dmc_count count;
> +	struct dmc_count *last = &dfi->last_event_count;
> +	u32 access = 0, total = 0;
> +	int i;
> +
> +	rockchip_dfi_read_counters(edev, &count);
> +
> +	/* We can only report one channel, so find the busiest one */
> +	for (i = 0; i < RK3399_DMC_NUM_CH; i++) {
> +		u32 a = count.c[i].access - last->c[i].access;
> +		u32 t = count.c[i].total - last->c[i].total;
> +
> +		if (a > access) {
> +			access = a;
> +			total = t;
> +		}
> +	}
>  
> -	busier_ch = rockchip_dfi_get_busier_ch(edev);
> +	edata->load_count = access * 4;
> +	edata->total_count = total;
>  
> -	edata->load_count = dfi->ch_usage[busier_ch].access * 4;
> -	edata->total_count = dfi->ch_usage[busier_ch].total;
> +	dfi->last_event_count = count;
>  
>  	return 0;
>  }

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