linux-kernel - Re: Tachometer speed returned rather than absolute fan speed?

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Message-ID: <20140307181718.GA1027@roeck-us.net>
Date:	Fri, 7 Mar 2014 10:17:18 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Laszlo Papp <lpapp@....org>
Cc:	Jean Delvare <jdelvare@...e.de>,
	LKML <linux-kernel@...r.kernel.org>, lm-sensors@...sensors.org
Subject: Re: Tachometer speed returned rather than absolute fan speed?

On Fri, Mar 07, 2014 at 03:47:08PM +0000, Laszlo Papp wrote:
> On Fri, Mar 7, 2014 at 3:37 PM, Jean Delvare <jdelvare@...e.de> wrote:
> >> > I'm quite confused. While I admit that the term "tachometer speed" is
> >> > awkward, the max6650 driver is reporting fan speeds in RPM as every
> >> > other hwmon driver. So I really have no idea what you think is wrong.
> >> > What did you think "tachometer speed" was, if not the fan speed? Does
> >> > the max6650 driver not return correct fan speeds for you?
> 
> That is some strange behavior. If I do "echo 1 > pwm1_enable; echo 0 >
> pwm1; cat fan1_input", I still see 30 for the connected fan, whereas I
> can see it stopped. Is this an expected behavior? I would expect zero
> as a user.
> 
I seem to recall that I had seen that as well, with no fan connected.
Maybe the tachometer registers always read at least '1'. I would think
it is wrong, but we'll have to understand the chip a bit better
to be able to provide a fix. Unless you already have a fix ready,
of course. I'll try to re-test tonight if I find the time.

Guenter
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