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SubjectRe: [PATCH RFC 3/3] hwmon: pwm-fan: Add RPM support via external interrupt
On Wed, Jan 30, 2019 at 04:07:07PM +0100, Stefan Wahren wrote:
> This adds RPM support to the pwm-fan driver in order to use with
> fancontrol/pwmconfig. This feature is intended for 2 pulse-per-revolution
> fans which provides a tachometer output signal.
>
> Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
> ---
> drivers/hwmon/pwm-fan.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 55 insertions(+)
>
> diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
> index 9e0591e..731fdc6 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>
> @@ -26,13 +27,22 @@
> #include <linux/regulator/consumer.h>
> #include <linux/sysfs.h>
> #include <linux/thermal.h>
> +#include <linux/timer.h>
>
> #define MAX_PWM 255
> +#define SAMPLE_TIME 1 /* seconds */
> +#define PULSE_PER_REVOLUTION 2
>
> struct pwm_fan_ctx {
> struct mutex lock;
> struct pwm_device *pwm;
> struct regulator *reg_en;
> +
> + int irq;
> + unsigned int pulses;
> + unsigned int rpm;
> + struct timer_list sample_timer;
> +
> unsigned int pwm_value;
> unsigned int pwm_fan_state;
> unsigned int pwm_fan_max_state;
> @@ -40,6 +50,27 @@ struct pwm_fan_ctx {
> struct thermal_cooling_device *cdev;
> };
>
> +static irqreturn_t pulse_handler(int irq, void *dev_id)
> +{
> + struct pwm_fan_ctx *ctx = dev_id;
> +
> + if (ctx->pulses < INT_MAX / 2)
> + ctx->pulses++;

Please explain the limit. With this code, the maximum number
for pulses is INT_MAX / 2. The calculation below multiplies
that with 60, which is well above UINT_MAX. Either use a
realistic limit or drop the if statement (it is kind of
unlikely to get that many interrupts per second).

> +
> + return IRQ_HANDLED;

This assumes a self resetting edge triggered interrupt ?
You might want to mention that somewhere.

> +}
> +
> +static void sample_timer(struct timer_list *t)
> +{
> + struct pwm_fan_ctx *ctx = from_timer(ctx, t, sample_timer);
> + unsigned int pulses;
> +
> + pulses = ctx->pulses;
> + ctx->pulses -= pulses;

This is racy; the substract operation is not atomic, and neither
is the addition in the interrupt handler.

> + ctx->rpm = pulses * 60 / SAMPLE_TIME / PULSE_PER_REVOLUTION;

The calculation assumes that sample_timer is called exactly after one
second. Have to tested how much variation this causes on a loaded system ?

> + mod_timer(&ctx->sample_timer, jiffies + (HZ * SAMPLE_TIME));
> +}
> +
> static int __set_pwm(struct pwm_fan_ctx *ctx, unsigned long pwm)
> {
> unsigned long period;
> @@ -100,11 +131,20 @@ 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,

This attribute is visible even if not supported, meaning it will
report a fan speed of 0 rpm in that case. Please make the attribute
conditional.

> NULL,
> };
>
> @@ -263,6 +303,19 @@ static int pwm_fan_probe(struct platform_device *pdev)
> }
> }
>
> + timer_setup(&ctx->sample_timer, sample_timer, 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");
> + return ret;
> + }
> + mod_timer(&ctx->sample_timer, jiffies + (HZ * SAMPLE_TIME));
> + }
> +
> hwmon = devm_hwmon_device_register_with_groups(&pdev->dev, "pwmfan",
> ctx, pwm_fan_groups);
> if (IS_ERR(hwmon)) {
> @@ -304,6 +357,8 @@ 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->sample_timer);
> +
> if (ctx->pwm_value)
> pwm_disable(ctx->pwm);
>

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