linux-kernel - Re: [PATCH v2 1/2] i8k: Autodetect maximal fan speed and fan RPM multiplier

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Date:	Sun, 21 Dec 2014 10:15:28 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Arnd Bergmann <arnd@...db.de>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, Valdis.Kletnieks@...edu,
	Steven Honeyman <stevenhoneyman@...il.com>,
	Jean Delvare <jdelvare@...e.de>,
	Gabriele Mazzotta <gabriele.mzt@...il.com>,
	Jochen Eisinger <jochen@...guin-breeder.org>
Subject: Re: [PATCH v2 1/2] i8k: Autodetect maximal fan speed and fan RPM multiplier

On Saturday 20 December 2014 20:02:31 Guenter Roeck wrote:
> > +		for (fan = 0; fan < ARRAY_SIZE(i8k_fan_mult); ++fan) {
> > +			i8k_fan_mult[fan] = I8K_FAN_DEFAULT_MULT;
> > +			if (i8k_get_fan_speed(fan) > I8K_FAN_MAX_RPM) {
> > +				i8k_fan_mult[fan] = 1;
> > +				continue;
> > +			}
> 
> Another note: On one of my systems, reading the current fan
> speed literally halts the entire system for a second or two.
> Given this, is the above really necessary ? It might be
> better to just try to use the nominal fan speeds and only
> read the actual fan speed if that doesn't work.
> 

Ok. I added fallback to i8k_get_fan_speed() only if function 
i8k_get_fan_nominal_speed() failed.

> > +			for (val = 0; val < 256; ++val) {
> > +				ret = i8k_get_fan_nominal_speed(fan, val);
> > +				if (ret > I8K_FAN_MAX_RPM) {
> > +					i8k_fan_mult[fan] = 1;
> > +					break;
> > +				} else if (ret < 0) {
> > +					break;
> > +				}
> > +			}
> 
> I wonder if it would help to detect the maximum fan speed
> first. Once that is known, it should be possible to just read
> the nominal fan speed once, for the known maximum speed. With
> this, the 'val' loop here would be unnecessary.
> 

Right, good point.

-- 
Pali Rohár
pali.rohar@...il.com

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