linux-kernel - Re: [PATCH v6] drm/i915/hwmon: expose fan speed

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Message-ID: <ZsSWTtew8nCYWrxF@black.fi.intel.com>
Date: Tue, 20 Aug 2024 16:12:46 +0300
From: Raag Jadav <raag.jadav@...el.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
	rodrigo.vivi@...el.com, tursulin@...ulin.net, airlied@...il.com,
	daniel@...ll.ch, linux@...ck-us.net, andi.shyti@...ux.intel.com,
	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
	anshuman.gupta@...el.com, badal.nilawar@...el.com,
	riana.tauro@...el.com, ashutosh.dixit@...el.com,
	karthik.poosa@...el.com
Subject: Re: [PATCH v6] drm/i915/hwmon: expose fan speed

On Tue, Aug 20, 2024 at 01:23:35PM +0300, Andy Shevchenko wrote:
> On Tue, Aug 20, 2024 at 11:50:10AM +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
> 
> > v2: Handle overflow, add mutex protection and ABI documentation
> >     Aesthetic adjustments (Riana)
> > v3: Change rotations data type, ABI date and version
> > v4: Fix wakeref leak
> >     Drop switch case and simplify hwm_fan_xx() (Andi)
> > v5: Rework time calculation, aesthetic adjustments (Andy)
> > v6: Drop overflow logic (Andy)
> >     Aesthetic adjustments (Badal)
> 
> But it still has an issue with 64-bit division on 32-bit platforms, right?
> 
> ...
> 
> > +	/*
> > +	 * Calculate fan speed in RPM by time averaging two subsequent
> > +	 * readings in minutes.
> > +	 * RPM = number of rotations * msecs per minute / time in msecs
> > +	 */
> > +	*val = DIV_ROUND_UP(rotations * (MSEC_PER_SEC * 60), time);
> 
> ...somewhere here?

Use div64_u64() instead? Or is there a better alternative?

Raag