Re: [PATCH V4 3/3] hwmon: pwm-fan: Add RPM support via external interrupt

[Guenter Roeck]

On Tue, Apr 02, 2019 at 04:21:50PM +0200, Stefan Wahren wrote:
> This adds RPM support to the pwm-fan driver in order to use with
> fancontrol/pwmconfig. This feature is intended for fans with a tachometer
> output signal, which generate a defined number of pulses per revolution.
> 
> Signed-off-by: Stefan Wahren <stefan.wahren@xxxxxxxx>
> ---
>  drivers/hwmon/pwm-fan.c | 111 ++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 107 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> index 167221c..3245a49 100644
> --- a/drivers/hwmon/pwm-fan.c
> +++ b/drivers/hwmon/pwm-fan.c
> @@ -18,6 +18,7 @@
>  
>  #include <linux/hwmon.h>
>  #include <linux/hwmon-sysfs.h>
> +#include <linux/interrupt.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
>  #include <linux/of.h>
> @@ -26,6 +27,7 @@
>  #include <linux/regulator/consumer.h>
>  #include <linux/sysfs.h>
>  #include <linux/thermal.h>
> +#include <linux/timer.h>
>  
>  #define MAX_PWM 255
>  
> @@ -33,6 +35,14 @@ struct pwm_fan_ctx {
>  	struct mutex lock;
>  	struct pwm_device *pwm;
>  	struct regulator *reg_en;
> +
> +	int irq;
> +	atomic_t pulses;
> +	unsigned int rpm;
> +	u8 pulses_per_revolution;
> +	ktime_t sample_start;
> +	struct timer_list rpm_timer;
> +
>  	unsigned int pwm_value;
>  	unsigned int pwm_fan_state;
>  	unsigned int pwm_fan_max_state;
> @@ -40,6 +50,32 @@ struct pwm_fan_ctx {
>  	struct thermal_cooling_device *cdev;
>  };
>  
> +/* This handler assumes self resetting edge triggered interrupt. */
> +static irqreturn_t pulse_handler(int irq, void *dev_id)
> +{
> +	struct pwm_fan_ctx *ctx = dev_id;
> +
> +	atomic_inc(&ctx->pulses);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static void sample_timer(struct timer_list *t)
> +{
> +	struct pwm_fan_ctx *ctx = from_timer(ctx, t, rpm_timer);
> +	int pulses;
> +	u64 tmp;
> +
> +	pulses = atomic_read(&ctx->pulses);
> +	atomic_sub(pulses, &ctx->pulses);
> +	tmp = (u64)pulses * ktime_ms_delta(ktime_get(), ctx->sample_start) * 60;
> +	do_div(tmp, ctx->pulses_per_revolution * 1000);
> +	ctx->rpm = tmp;
> +
> +	ctx->sample_start = ktime_get();
> +	mod_timer(&ctx->rpm_timer, jiffies + HZ);
> +}
> +
>  static int  __set_pwm(struct pwm_fan_ctx *ctx, unsigned long pwm)
>  {
>  	unsigned long period;
> @@ -100,15 +136,49 @@ static ssize_t pwm_show(struct device *dev, struct device_attribute *attr,
>  	return sprintf(buf, "%u\n", ctx->pwm_value);
>  }
>  
> +static ssize_t rpm_show(struct device *dev,
> +			struct device_attribute *attr, char *buf)
> +{
> +	struct pwm_fan_ctx *ctx = dev_get_drvdata(dev);
> +
> +	return sprintf(buf, "%u\n", ctx->rpm);
> +}
>  
>  static SENSOR_DEVICE_ATTR_RW(pwm1, pwm, 0);
> +static SENSOR_DEVICE_ATTR_RO(fan1_input, rpm, 0);
>  
>  static struct attribute *pwm_fan_attrs[] = {
>  	&sensor_dev_attr_pwm1.dev_attr.attr,
> +	&sensor_dev_attr_fan1_input.dev_attr.attr,
>  	NULL,
>  };
>  
> -ATTRIBUTE_GROUPS(pwm_fan);
> +static umode_t pwm_fan_attrs_visible(struct kobject *kobj, struct attribute *a,
> +				     int n)
> +{
> +	struct device *dev = container_of(kobj, struct device, kobj);
> +	struct pwm_fan_ctx *ctx = dev_get_drvdata(dev);
> +	struct device_attribute *devattr;
> +
> +	/* Hide fan_input in case no interrupt is available  */
> +	devattr = container_of(a, struct device_attribute, attr);
> +	if (devattr == &sensor_dev_attr_fan1_input.dev_attr) {
> +		if (ctx->irq <= 0)
> +			return 0;
> +	}

Side note: This can be easier written as 
	if (n == 1 && ctx->irq <= 0)
		return 0;

Not that it matters much.

> +
> +	return a->mode;
> +}
> +
> +static const struct attribute_group pwm_fan_group = {
> +	.attrs = pwm_fan_attrs,
> +	.is_visible = pwm_fan_attrs_visible,
> +};
> +
> +static const struct attribute_group *pwm_fan_groups[] = {
> +	&pwm_fan_group,
> +	NULL,
> +};
>  
>  /* thermal cooling device callbacks */
>  static int pwm_fan_get_max_state(struct thermal_cooling_device *cdev,
> @@ -261,17 +331,45 @@ static int pwm_fan_probe(struct platform_device *pdev)
>  		goto err_reg_disable;
>  	}
>  
> +	timer_setup(&ctx->rpm_timer, sample_timer, 0);
> +
> +	if (of_property_read_u8(pdev->dev.of_node, "pulses-per-revolution",

This does not work: The property is not defined as u8. You have to either
use of_property_read_u32() or declare the property as u8.

[ Sorry, I didn't know until recently that this is necessary ]

> +				&ctx->pulses_per_revolution)) {
> +		ctx->pulses_per_revolution = 2;
> +	}
> +
> +	if (!ctx->pulses_per_revolution) {
> +		dev_err(&pdev->dev, "pulses-per-revolution can't be zero.\n");
> +		ret = -EINVAL;
> +		goto err_pwm_disable;
> +	}
> +
> +	ctx->irq = platform_get_irq(pdev, 0);
> +	if (ctx->irq == -EPROBE_DEFER) {
> +		ret = ctx->irq;
> +		goto err_pwm_disable;

It might be better to call platform_get_irq() and to do do this check
first, before enabling the regulator (in practice before calling
devm_regulator_get_optional). It doesn't make sense to enable the
regulator only to disable it because the irq is not yet available.

> +	} else if (ctx->irq > 0) {

As written, this else is unnecessary, and static checkers will complain
about it.

> +		ret = devm_request_irq(&pdev->dev, ctx->irq, pulse_handler, 0,
> +				       pdev->name, ctx);
> +		if (ret) {
> +			dev_err(&pdev->dev, "Can't get interrupt working.\n");
> +			goto err_pwm_disable;
> +		}
> +		ctx->sample_start = ktime_get();
> +		mod_timer(&ctx->rpm_timer, jiffies + HZ);
> +	}
> +
>  	hwmon = devm_hwmon_device_register_with_groups(&pdev->dev, "pwmfan",
>  						       ctx, pwm_fan_groups);
>  	if (IS_ERR(hwmon)) {
>  		dev_err(&pdev->dev, "Failed to register hwmon device\n");
>  		ret = PTR_ERR(hwmon);
> -		goto err_pwm_disable;
> +		goto err_del_timer;
>  	}
>  
>  	ret = pwm_fan_of_get_cooling_data(&pdev->dev, ctx);
>  	if (ret)
> -		return ret;
> +		goto err_del_timer;

Outch. This is buggy and should have been "goto err_pwm_disable;".
It needs to be fixed with a separate patch, and first, so we can
backport it. Can you do that ?

>  
>  	ctx->pwm_fan_state = ctx->pwm_fan_max_state;
>  	if (IS_ENABLED(CONFIG_THERMAL)) {
> @@ -282,7 +380,7 @@ static int pwm_fan_probe(struct platform_device *pdev)
>  			dev_err(&pdev->dev,
>  				"Failed to register pwm-fan as cooling device");
>  			ret = PTR_ERR(cdev);
> -			goto err_pwm_disable;
> +			goto err_del_timer;
>  		}
>  		ctx->cdev = cdev;
>  		thermal_cdev_update(cdev);
> @@ -290,6 +388,9 @@ static int pwm_fan_probe(struct platform_device *pdev)
>  
>  	return 0;
>  
> +err_del_timer:
> +	del_timer_sync(&ctx->rpm_timer);
> +
>  err_pwm_disable:
>  	state.enabled = false;
>  	pwm_apply_state(ctx->pwm, &state);
> @@ -306,6 +407,8 @@ static int pwm_fan_remove(struct platform_device *pdev)
>  	struct pwm_fan_ctx *ctx = platform_get_drvdata(pdev);
>  
>  	thermal_cooling_device_unregister(ctx->cdev);
> +	del_timer_sync(&ctx->rpm_timer);
> +
>  	if (ctx->pwm_value)
>  		pwm_disable(ctx->pwm);
>  
> -- 
> 2.7.4
>