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Date: Fri, 29 Mar 2019 16:02:12 +0000
From: Robin Murphy <robin.murphy@....com>
To: Stefan Wahren <stefan.wahren@...e.com>,
Kamil Debski <kamil@...as.org>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
Jean Delvare <jdelvare@...e.com>,
Guenter Roeck <linux@...ck-us.net>,
Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>
Cc: linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 3/3] hwmon: pwm-fan: Add RPM support via external
interrupt
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@...e.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);
>
>
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