Re: [PATCH 2/3] hwmon: bt1-pvt: Cache current update timeout

[Guenter Roeck <linux@roeck-us.net>]

On Sun, Sep 20, 2020 at 02:09:22PM +0300, Serge Semin wrote:
> Instead of converting the update timeout data to the milliseconds each
> time on the read procedure let's preserve the currently set timeout in the
> dedicated driver private data cache. The cached value will be then used in
> the timeout read method and in the alarm-less data conversion to prevent
> the caller task hanging up in case if the PVT sensor is suddenly powered
> down.
> 
> Fixes: 87976ce2825d ("hwmon: Add Baikal-T1 PVT sensor driver")
> Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>

Applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/bt1-pvt.c | 85 ++++++++++++++++++++++-------------------
>  drivers/hwmon/bt1-pvt.h |  3 ++
>  2 files changed, 49 insertions(+), 39 deletions(-)
> 
> diff --git a/drivers/hwmon/bt1-pvt.c b/drivers/hwmon/bt1-pvt.c
> index f4b7353c078a..2600426a3b21 100644
> --- a/drivers/hwmon/bt1-pvt.c
> +++ b/drivers/hwmon/bt1-pvt.c
> @@ -655,44 +655,16 @@ static int pvt_write_trim(struct pvt_hwmon *pvt, long val)
>  
>  static int pvt_read_timeout(struct pvt_hwmon *pvt, long *val)
>  {
> -	unsigned long rate;
> -	ktime_t kt;
> -	u32 data;
> -
> -	rate = clk_get_rate(pvt->clks[PVT_CLOCK_REF].clk);
> -	if (!rate)
> -		return -ENODEV;
> -
> -	/*
> -	 * Don't bother with mutex here, since we just read data from MMIO.
> -	 * We also have to scale the ticks timeout up to compensate the
> -	 * ms-ns-data translations.
> -	 */
> -	data = readl(pvt->regs + PVT_TTIMEOUT) + 1;
> +	int ret;
>  
> -	/*
> -	 * Calculate ref-clock based delay (Ttotal) between two consecutive
> -	 * data samples of the same sensor. So we first must calculate the
> -	 * delay introduced by the internal ref-clock timer (Tref * Fclk).
> -	 * Then add the constant timeout cuased by each conversion latency
> -	 * (Tmin). The basic formulae for each conversion is following:
> -	 *   Ttotal = Tref * Fclk + Tmin
> -	 * Note if alarms are enabled the sensors are polled one after
> -	 * another, so in order to have the delay being applicable for each
> -	 * sensor the requested value must be equally redistirbuted.
> -	 */
> -#if defined(CONFIG_SENSORS_BT1_PVT_ALARMS)
> -	kt = ktime_set(PVT_SENSORS_NUM * (u64)data, 0);
> -	kt = ktime_divns(kt, rate);
> -	kt = ktime_add_ns(kt, PVT_SENSORS_NUM * PVT_TOUT_MIN);
> -#else
> -	kt = ktime_set(data, 0);
> -	kt = ktime_divns(kt, rate);
> -	kt = ktime_add_ns(kt, PVT_TOUT_MIN);
> -#endif
> +	ret = mutex_lock_interruptible(&pvt->iface_mtx);
> +	if (ret)
> +		return ret;
>  
>  	/* Return the result in msec as hwmon sysfs interface requires. */
> -	*val = ktime_to_ms(kt);
> +	*val = ktime_to_ms(pvt->timeout);
> +
> +	mutex_unlock(&pvt->iface_mtx);
>  
>  	return 0;
>  }
> @@ -700,7 +672,7 @@ static int pvt_read_timeout(struct pvt_hwmon *pvt, long *val)
>  static int pvt_write_timeout(struct pvt_hwmon *pvt, long val)
>  {
>  	unsigned long rate;
> -	ktime_t kt;
> +	ktime_t kt, cache;
>  	u32 data;
>  	int ret;
>  
> @@ -713,7 +685,7 @@ static int pvt_write_timeout(struct pvt_hwmon *pvt, long val)
>  	 * between all available sensors to have the requested delay
>  	 * applicable to each individual sensor.
>  	 */
> -	kt = ms_to_ktime(val);
> +	cache = kt = ms_to_ktime(val);
>  #if defined(CONFIG_SENSORS_BT1_PVT_ALARMS)
>  	kt = ktime_divns(kt, PVT_SENSORS_NUM);
>  #endif
> @@ -742,6 +714,7 @@ static int pvt_write_timeout(struct pvt_hwmon *pvt, long val)
>  		return ret;
>  
>  	pvt_set_tout(pvt, data);
> +	pvt->timeout = cache;
>  
>  	mutex_unlock(&pvt->iface_mtx);
>  
> @@ -1018,10 +991,17 @@ static int pvt_check_pwr(struct pvt_hwmon *pvt)
>  	return ret;
>  }
>  
> -static void pvt_init_iface(struct pvt_hwmon *pvt)
> +static int pvt_init_iface(struct pvt_hwmon *pvt)
>  {
> +	unsigned long rate;
>  	u32 trim, temp;
>  
> +	rate = clk_get_rate(pvt->clks[PVT_CLOCK_REF].clk);
> +	if (!rate) {
> +		dev_err(pvt->dev, "Invalid reference clock rate\n");
> +		return -ENODEV;
> +	}
> +
>  	/*
>  	 * Make sure all interrupts and controller are disabled so not to
>  	 * accidentally have ISR executed before the driver data is fully
> @@ -1036,12 +1016,37 @@ static void pvt_init_iface(struct pvt_hwmon *pvt)
>  	pvt_set_mode(pvt, pvt_info[pvt->sensor].mode);
>  	pvt_set_tout(pvt, PVT_TOUT_DEF);
>  
> +	/*
> +	 * Preserve the current ref-clock based delay (Ttotal) between the
> +	 * sensors data samples in the driver data so not to recalculate it
> +	 * each time on the data requests and timeout reads. It consists of the
> +	 * delay introduced by the internal ref-clock timer (N / Fclk) and the
> +	 * constant timeout caused by each conversion latency (Tmin):
> +	 *   Ttotal = N / Fclk + Tmin
> +	 * If alarms are enabled the sensors are polled one after another and
> +	 * in order to get the next measurement of a particular sensor the
> +	 * caller will have to wait for at most until all the others are
> +	 * polled. In that case the formulae will look a bit different:
> +	 *   Ttotal = 5 * (N / Fclk + Tmin)
> +	 */
> +#if defined(CONFIG_SENSORS_BT1_PVT_ALARMS)
> +	pvt->timeout = ktime_set(PVT_SENSORS_NUM * PVT_TOUT_DEF, 0);
> +	pvt->timeout = ktime_divns(pvt->timeout, rate);
> +	pvt->timeout = ktime_add_ns(pvt->timeout, PVT_SENSORS_NUM * PVT_TOUT_MIN);
> +#else
> +	pvt->timeout = ktime_set(PVT_TOUT_DEF, 0);
> +	pvt->timeout = ktime_divns(pvt->timeout, rate);
> +	pvt->timeout = ktime_add_ns(pvt->timeout, PVT_TOUT_MIN);
> +#endif
> +
>  	trim = PVT_TRIM_DEF;
>  	if (!of_property_read_u32(pvt->dev->of_node,
>  	     "baikal,pvt-temp-offset-millicelsius", &temp))
>  		trim = pvt_calc_trim(temp);
>  
>  	pvt_set_trim(pvt, trim);
> +
> +	return 0;
>  }
>  
>  static int pvt_request_irq(struct pvt_hwmon *pvt)
> @@ -1149,7 +1154,9 @@ static int pvt_probe(struct platform_device *pdev)
>  	if (ret)
>  		return ret;
>  
> -	pvt_init_iface(pvt);
> +	ret = pvt_init_iface(pvt);
> +	if (ret)
> +		return ret;
>  
>  	ret = pvt_request_irq(pvt);
>  	if (ret)
> diff --git a/drivers/hwmon/bt1-pvt.h b/drivers/hwmon/bt1-pvt.h
> index 5eac73e94885..93b8dd5e7c94 100644
> --- a/drivers/hwmon/bt1-pvt.h
> +++ b/drivers/hwmon/bt1-pvt.h
> @@ -10,6 +10,7 @@
>  #include <linux/completion.h>
>  #include <linux/hwmon.h>
>  #include <linux/kernel.h>
> +#include <linux/ktime.h>
>  #include <linux/mutex.h>
>  #include <linux/seqlock.h>
>  
> @@ -201,6 +202,7 @@ struct pvt_cache {
>   *	       if alarms are disabled).
>   * @sensor: current PVT sensor the data conversion is being performed for.
>   * @cache: data cache descriptor.
> + * @timeout: conversion timeout cache.
>   */
>  struct pvt_hwmon {
>  	struct device *dev;
> @@ -214,6 +216,7 @@ struct pvt_hwmon {
>  	struct mutex iface_mtx;
>  	enum pvt_sensor_type sensor;
>  	struct pvt_cache cache[PVT_SENSORS_NUM];
> +	ktime_t timeout;
>  };
>  
>  /*