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

[Robin Murphy <robin.murphy@arm.com>]

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@i2se.com>
>>> ---
>>>   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;

>>
>> [ 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?

Robin.

>>> +		}
>>> +		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)) {
>>>   		dev_err(&pdev->dev, "Failed to register hwmon device\n");
>>>   		ret = PTR_ERR(hwmon);
>>> -		goto err_pwm_disable;
>>> +		goto err_del_timer;
>>>   	}
>>>   
>>>   	ret = pwm_fan_of_get_cooling_data(&pdev->dev, ctx);
>>>   	if (ret)
>>> -		return ret;
>>> +		goto err_del_timer;
>> Outch. This is buggy and should have been "goto err_pwm_disable;".
>> It needs to be fixed with a separate patch, and first, so we can
>> backport it. Can you do that ?
> 
> Sure
> 
> Stefan
>