[PATCH V3 0/3] hwmon: pwm-fan: Add RPM support

[PATCH V3 0/3] hwmon: pwm-fan: Add RPM support

[Stefan Wahren]

Contrary to the gpio-fan the pwm-fan driver isn't easy to setup
with pwmconfig/fancontrol because of the missing hwmon sysfs entry
for actual revolutions per minute. This series adds this feature.

Changes in V3:
- rename property interrupt-ratio to pulses-per-revolution
  to avoid confusion with interrupt binding
- handle error case pulses-per-revolution = 0
- bail out properly in case we are unable to request the irq

Changes in V2:
- address Guenter's comments:
  - improve description of interrupts
  - use atomic_t to avoid races of the pulse counter
  - measure sample time to make rpm more reliable under load
  - make sysfs entry fan1_input conditional
- add dt-property to define interrupts per fan revolution
- example for fan with RPM support


Stefan Wahren (3):
  dt-bindings: hwmon: Add tachometer interrupt to pwm-fan
  Documentation: pwm-fan: Add description for RPM support
  hwmon: pwm-fan: Add RPM support via external interrupt

 .../devicetree/bindings/hwmon/pwm-fan.txt          |  22 ++++-
 Documentation/hwmon/pwm-fan                        |   3 +
 drivers/hwmon/pwm-fan.c                            | 100 ++++++++++++++++++++-
 3 files changed, 123 insertions(+), 2 deletions(-)

-- 
2.7.4

[PATCH V3 1/3] dt-bindings: hwmon: Add tachometer interrupt to pwm-fan

[Stefan Wahren]

This adds the tachometer interrupt to the pwm-fan binding, which is
necessary for RPM support.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 .../devicetree/bindings/hwmon/pwm-fan.txt          | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.txt b/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
index 49ca5d8..722005f 100644
--- a/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
+++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
@@ -7,7 +7,16 @@ Required properties:
 			which correspond to thermal cooling states
 
 Optional properties:
-- fan-supply    : phandle to the regulator that provides power to the fan
+- fan-supply		: phandle to the regulator that provides power to the fan
+- interrupts		: This contains a single interrupt specifier which
+			  describes the tachometer output of the fan as an
+			  interrupt source. The output signal must generate a
+			  defined number of interrupts per fan revolution, which
+			  require that it must be self resetting edge interrupts.
+			  See interrupt-controller/interrupts.txt for the format.
+- pulses-per-revolution : define the tachometer pulses per fan revolution as
+			  an integer (default is 2 interrupts per revolution).
+			  The value must be greater than zero.
 
 Example:
 	fan0: pwm-fan {
@@ -38,3 +47,14 @@ Example:
 					};
 			     };
 		};
+
+Example 2:
+	fan0: pwm-fan {
+		fan0: pwm-fan {
+		compatible = "pwm-fan";
+		pwms = <&pwm 0 40000 0>;
+		fan-supply = <&reg_fan>;
+		interrupt-parent = <&gpio5>;
+		interrupts = <1 IRQ_TYPE_EDGE_FALLING>;
+		pulses-per-revolution = <2>;
+	};
-- 
2.7.4

Re: [PATCH V3 1/3] dt-bindings: hwmon: Add tachometer interrupt to pwm-fan

[Rob Herring]

On Fri, Mar 22, 2019 at 09:24:01AM +0100, Stefan Wahren wrote:
> This adds the tachometer interrupt to the pwm-fan binding, which is
> necessary for RPM support.
> 
> Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
> ---
>  .../devicetree/bindings/hwmon/pwm-fan.txt          | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.txt b/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
> index 49ca5d8..722005f 100644
> --- a/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
> +++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.txt
> @@ -7,7 +7,16 @@ Required properties:
>  			which correspond to thermal cooling states
>  
>  Optional properties:
> -- fan-supply    : phandle to the regulator that provides power to the fan
> +- fan-supply		: phandle to the regulator that provides power to the fan
> +- interrupts		: This contains a single interrupt specifier which
> +			  describes the tachometer output of the fan as an
> +			  interrupt source. The output signal must generate a
> +			  defined number of interrupts per fan revolution, which
> +			  require that it must be self resetting edge interrupts.
> +			  See interrupt-controller/interrupts.txt for the format.
> +- pulses-per-revolution : define the tachometer pulses per fan revolution as
> +			  an integer (default is 2 interrupts per revolution).
> +			  The value must be greater than zero.
>  
>  Example:
>  	fan0: pwm-fan {
> @@ -38,3 +47,14 @@ Example:
>  					};
>  			     };
>  		};
> +
> +Example 2:
> +	fan0: pwm-fan {
> +		fan0: pwm-fan {

This line should go.

Otherwise,

Reviewed-by: Rob Herring <robh@kernel.org>

> +		compatible = "pwm-fan";
> +		pwms = <&pwm 0 40000 0>;
> +		fan-supply = <&reg_fan>;
> +		interrupt-parent = <&gpio5>;
> +		interrupts = <1 IRQ_TYPE_EDGE_FALLING>;
> +		pulses-per-revolution = <2>;
> +	};
> -- 
> 2.7.4
> 

[PATCH V3 2/3] Documentation: pwm-fan: Add description for RPM support

[Stefan Wahren]

This adds a short description for the new RPM support of the pwm-fan
driver.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
---
 Documentation/hwmon/pwm-fan | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/hwmon/pwm-fan b/Documentation/hwmon/pwm-fan
index 18529d2..82fe967 100644
--- a/Documentation/hwmon/pwm-fan
+++ b/Documentation/hwmon/pwm-fan
@@ -15,3 +15,6 @@ The driver implements a simple interface for driving a fan connected to
 a PWM output. It uses the generic PWM interface, thus it can be used with
 a range of SoCs. The driver exposes the fan to the user space through
 the hwmon's sysfs interface.
+
+The fan rotation speed returned via the optional 'fan1_input' is extrapolated
+from the sampled interrupts from the tachometer signal within 1 second.
-- 
2.7.4

[PATCH V3 3/3] hwmon: pwm-fan: Add RPM support via external interrupt

[Stefan Wahren]

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@i2se.com>
---
 drivers/hwmon/pwm-fan.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 99 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
index 167221c..c8fb6a3 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;
+	u32 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;
+
+	/* Avoid possible overflow */
+	if (atomic_read(&ctx->pulses) < 100000)
+		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, sample_ms;
+
+	pulses = atomic_read(&ctx->pulses);
+	atomic_sub(pulses, &ctx->pulses);
+	sample_ms = ktime_ms_delta(ktime_get(), ctx->sample_start);
+	ctx->rpm = pulses * 60 * sample_ms / 1000 / ctx->pulses_per_revolution;
+
+	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;
+	}
+
+	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,
@@ -261,6 +331,32 @@ 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_u32(pdev->dev.of_node, "pulses-per-revolution",
+				 &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;
+	}
+
+	atomic_set(&ctx->pulses, 0);
+	ctx->irq = platform_get_irq(pdev, 0);
+	if (ctx->irq >= 0) {
+		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)) {
@@ -306,6 +402,8 @@ 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

Re: [PATCH V3 3/3] hwmon: pwm-fan: Add RPM support via external interrupt

[Guenter Roeck]

On 3/22/19 1:24 AM, 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@i2se.com>
> ---
>   drivers/hwmon/pwm-fan.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 99 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> index 167221c..c8fb6a3 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;
> +	u32 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;
> +
> +	/* Avoid possible overflow */
> +	if (atomic_read(&ctx->pulses) < 100000)
> +		atomic_inc(&ctx->pulses);
> +

100000 * 60 * 1000 = 6,000,000,000, which is already above 32 bit,
so you still get the overflow.

Any limit would have to be below (0xffffffff / (60 * sample_ms))
for the maximum expected value of sample_ms.

You could select a working limit, such as 32768 (that is just as arbitrary
as 100,000, but at least it works up to sample_ms above 2,000), or check
for overflow when calculating rpm.

> +	return IRQ_HANDLED;
> +}
> +
> +static void sample_timer(struct timer_list *t)
> +{
> +	struct pwm_fan_ctx *ctx = from_timer(ctx, t, rpm_timer);
> +	int pulses, sample_ms;
> +
> +	pulses = atomic_read(&ctx->pulses);
> +	atomic_sub(pulses, &ctx->pulses);
> +	sample_ms = ktime_ms_delta(ktime_get(), ctx->sample_start);
> +	ctx->rpm = pulses * 60 * sample_ms / 1000 / ctx->pulses_per_revolution;
> +
> +	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;
> +	}
> +
> +	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,
> @@ -261,6 +331,32 @@ 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_u32(pdev->dev.of_node, "pulses-per-revolution",
> +				 &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;
> +	}
> +
> +	atomic_set(&ctx->pulses, 0);

Already initialized with 0.

> +	ctx->irq = platform_get_irq(pdev, 0);
> +	if (ctx->irq >= 0) {

I have seen other patches recently, changing this check to > 0.
I never know what a valid irq is, but it may be prudent to change this to > 0
(and the check in is_visible to <= 0).

Either case, the function can return -EPROBE_DEFER, which should be handled
and not be ignored.

> +		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)) {

del_timer_sync() here ?

> @@ -306,6 +402,8 @@ 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);
>   
> 

Re: [PATCH V3 3/3] hwmon: pwm-fan: Add RPM support via external interrupt

[Robin Murphy]

On 22/03/2019 08:24, 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.

Thanks for the CC - this is something I was planning to play with now 
that I have my fan set up, so it's nice to find it already done :)

My board has a 3-wire fan connector driven by an unfiltered PWM output, 
so unfortunately what I end up measuring is actually the PWM frequency 
modulated by the rotation pulse frequency. I hacked up some crude 
low-pass filtering which subsequently got lost in a git reset incident, 
but I could recreate it if you think it's an idea worth considering 
(from a bit of research it does seem that 2 or 3-wire fans aren't really 
meant to be PWMed that way).

> Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
> ---
>   drivers/hwmon/pwm-fan.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 99 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> index 167221c..c8fb6a3 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;
> +	u32 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;
> +
> +	/* Avoid possible overflow */
> +	if (atomic_read(&ctx->pulses) < 100000)

I agree with Guenter that this seems a bit misplaced - since the raw 
count itself is unlikely to overflow in practice, it certainly feels 
more sensible to handle calculation overflow in the calculation itself...

> +		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, sample_ms;
> +
> +	pulses = atomic_read(&ctx->pulses);
> +	atomic_sub(pulses, &ctx->pulses);
> +	sample_ms = ktime_ms_delta(ktime_get(), ctx->sample_start);
> +	ctx->rpm = pulses * 60 * sample_ms / 1000 / ctx->pulses_per_revolution;

...for which maybe mult_frac() could help here, although it might be 
easier just to do the intermediate calculations in u64 and arrange them 
to rule out non-constant division.

Robin.

> +
> +	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;
> +	}
> +
> +	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,
> @@ -261,6 +331,32 @@ 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_u32(pdev->dev.of_node, "pulses-per-revolution",
> +				 &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;
> +	}
> +
> +	atomic_set(&ctx->pulses, 0);
> +	ctx->irq = platform_get_irq(pdev, 0);
> +	if (ctx->irq >= 0) {
> +		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)) {
> @@ -306,6 +402,8 @@ 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);
>   
>