linux-kernel - Re: [PATCH 04/13] thermal/drivers/hisi: Simplify the temperature/step computation

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Date:   Fri, 1 Sep 2017 22:24:48 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     rui.zhang@...el.com, edubezval@...il.com, linux-pm@...r.kernel.org,
        kevin.wangtao@...aro.org, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/13] thermal/drivers/hisi: Simplify the
 temperature/step computation

On Wed, Aug 30, 2017 at 10:47:28AM +0200, Daniel Lezcano wrote:
> The step and the base temperature are fixed values, we can simplify the
> computation by converting the base temperature to milli celsius and use a
> pre-computed step value. That saves us a lot of mult + div for nothing at
> runtime.
> 
> Take also the opportunity to change the function names to be consistent with
> the rest of the code.
> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>

Reviewed-by: Leo Yan <leo.yan@...aro.org>
Tested-by: Leo Yan <leo.yan@...aro.org>

> ---
>  drivers/thermal/hisi_thermal.c | 41 ++++++++++++++++++++++++++++-------------
>  1 file changed, 28 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/thermal/hisi_thermal.c b/drivers/thermal/hisi_thermal.c
> index 67db523..b58ad40 100644
> --- a/drivers/thermal/hisi_thermal.c
> +++ b/drivers/thermal/hisi_thermal.c
> @@ -35,8 +35,9 @@
>  #define TEMP0_RST_MSK			(0x1C)
>  #define TEMP0_VALUE			(0x28)
>  
> -#define HISI_TEMP_BASE			(-60)
> +#define HISI_TEMP_BASE			(-60000)
>  #define HISI_TEMP_RESET			(100000)
> +#define HISI_TEMP_STEP			(784)
>  
>  #define HISI_MAX_SENSORS		4
>  #define HISI_DEFAULT_SENSOR		2
> @@ -61,19 +62,32 @@ struct hisi_thermal_data {
>  	void __iomem *regs;
>  };
>  
> -/* in millicelsius */
> -static inline int _step_to_temp(int step)
> +/*
> + * The temperature computation on the tsensor is as follow:
> + *	Unit: millidegree Celsius
> + *	Step: 255/200 (0.7843)
> + *	Temperature base: -60°C
> + *
> + * The register is programmed in temperature steps, every step is 784
> + * millidegree and begins at -60 000 m°C
> + *
> + * The temperature from the steps:
> + *
> + *	Temp = TempBase + (steps x 784)
> + *
> + * and the steps from the temperature:
> + *
> + *	steps = (Temp - TempBase) / 784
> + *
> + */
> +static inline int hisi_thermal_step_to_temp(int step)
>  {
> -	/*
> -	 * Every step equals (1 * 200) / 255 celsius, and finally
> -	 * need convert to millicelsius.
> -	 */
> -	return (HISI_TEMP_BASE * 1000 + (step * 200000 / 255));
> +	return HISI_TEMP_BASE + (step * HISI_TEMP_STEP);
>  }
>  
> -static inline long _temp_to_step(long temp)
> +static inline long hisi_thermal_temp_to_step(long temp)
>  {
> -	return ((temp - HISI_TEMP_BASE * 1000) * 255) / 200000;
> +	return (temp - HISI_TEMP_BASE) / HISI_TEMP_STEP;
>  }
>  
>  static long hisi_thermal_get_sensor_temp(struct hisi_thermal_data *data,
> @@ -99,7 +113,7 @@ static long hisi_thermal_get_sensor_temp(struct hisi_thermal_data *data,
>  	usleep_range(3000, 5000);
>  
>  	val = readl(data->regs + TEMP0_VALUE);
> -	val = _step_to_temp(val);
> +	val = hisi_thermal_step_to_temp(val);
>  
>  	mutex_unlock(&data->thermal_lock);
>  
> @@ -126,10 +140,11 @@ static void hisi_thermal_enable_bind_irq_sensor
>  	writel((sensor->id << 12), data->regs + TEMP0_CFG);
>  
>  	/* enable for interrupt */
> -	writel(_temp_to_step(sensor->thres_temp) | 0x0FFFFFF00,
> +	writel(hisi_thermal_temp_to_step(sensor->thres_temp) | 0x0FFFFFF00,
>  	       data->regs + TEMP0_TH);
>  
> -	writel(_temp_to_step(HISI_TEMP_RESET), data->regs + TEMP0_RST_TH);
> +	writel(hisi_thermal_temp_to_step(HISI_TEMP_RESET),
> +	       data->regs + TEMP0_RST_TH);
>  
>  	/* enable module */
>  	writel(0x1, data->regs + TEMP0_RST_MSK);
> -- 
> 2.7.4
>