Re: [PATCH V3 3/3] hwmon: pwm-fan: Add RPM support via external interrupt
From: Robin Murphy
Date: Fri Mar 29 2019 - 12:02:19 EST
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@xxxxxxxx>
---
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);