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

[Stefan Wahren <stefan.wahren@xxxxxxxx>]

Am 03.04.2019 um 17:59 schrieb Robin Murphy:
> On 03/04/2019 10:55, Stefan Wahren wrote:
> > Hi Guenter,
> >
> > Am 02.04.19 um 22:55 schrieb 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.
> > pulses_per_revolution is defined as u8 since this version
>
> The variable might be, but the "pulses-per-revolution" property itself 
> is not being defined with the appropriate DT type ("/bits/ 8") in the 
> binding, and thus will be stored as a regular 32-bit cell, for which 
> reading it as a u8 array may or may not work correctly depending on 
> endianness.
>
> TBH, unless there's a real need for a specific binary format in the 
> FDT, I don't think it's usually worth the bother of using irregular DT 
> types, especially when the practical impact amounts to possibly saving 
> up to 3 bytes for a property which usually won't need to be specified 
> anyway. I'd just do something like:
>
>     u32 ppr = 2;
>
>     of_property_read_u32(np, "pulses-per-revolution", &ppr);
>     ctx->pulses_per_revolution = ppr;

My intention was to avoid another overflow in case the device tree 
provides unrealistic values ( my expected range 1 - 10 ). Saving space 
would be a benefit, but i'm okay with this suggestion.

> > > [ 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;
>
> We could still continue without RPM support at this point, couldn't 
> we? Or is this a deliberate "if that failed, then who knows how messed 
> up the system is..." kind of thing?

In case someone specified an interrupt, the user expect it to work. This 
helps to identify broken DT faster.

The gpio-fan also have optional irq support and also bail out if 
devm_request_irq fails.

Btw i will add the return code into the error message.

Stefan