Re: [PATCH v5] drm/i915/hwmon: expose fan speed

[Raag Jadav <raag.jadav@intel.com>]

On Mon, Aug 12, 2024 at 04:15:14PM +0300, Andy Shevchenko wrote:
> On Mon, Aug 12, 2024 at 01:45:38PM +0530, Raag Jadav wrote:
> > Add hwmon support for fan1_input attribute, which will expose fan speed
> > in RPM. With this in place we can monitor fan speed using lm-sensors tool.
> > 
> > $ sensors
> > i915-pci-0300
> > Adapter: PCI adapter
> > in0:         653.00 mV
> > fan1:        3833 RPM
> > power1:           N/A  (max =  43.00 W)
> > energy1:      32.02 kJ
> 
> ...
> 
> > +static int
> > +hwm_fan_read(struct hwm_drvdata *ddat, u32 attr, long *val)
> > +{
> > +	struct i915_hwmon *hwmon = ddat->hwmon;
> > +	struct hwm_fan_info *fi = &ddat->fi;
> > +	u64 rotations, time_now, time;
> > +	intel_wakeref_t wakeref;
> > +	u32 reg_val, pulses;
> > +	int ret = 0;
> > +
> > +	if (attr != hwmon_fan_input)
> > +		return -EOPNOTSUPP;
> > +
> > +	wakeref = intel_runtime_pm_get(ddat->uncore->rpm);
> > +	mutex_lock(&hwmon->hwmon_lock);
> > +
> > +	reg_val = intel_uncore_read(ddat->uncore, hwmon->rg.fan_speed);
> > +	time_now = get_jiffies_64();
> 
> > +	/* Handle HW register overflow */
> > +	if (reg_val >= fi->reg_val_prev)
> > +		pulses = reg_val - fi->reg_val_prev;
> > +	else
> > +		pulses = UINT_MAX - fi->reg_val_prev + reg_val;
> 
> Isn't it the abs_diff() reimplementation?

Not exactly. This is specific to 32 bit register overflow, so we count
from max value.

Raag