[lm-sensors] it87.fix_pwm_polarity

[lm-sensors] it87.fix_pwm_polarity

[Ian Pilcher]

I am setting up a Thecus N5550 NAS, and I found that the it87 driver
disables PWM control of the drive bay fan (it87.656/pwm3) unless I pass
the fix_pwm_polarity parameter.  Once I add that parameter, fan control
appears to work just fine.

Does this setting actually invert the voltage that is supplied to the
fan?  If so, does this have the potential to damage the fan itself (or
other components)?

Note that Thecus provides their own Linux-based "firmware" for this
NAS, so it's unlikely that they will ever change the way the BIOS sets
up the fans.  (And having the drive bay fan off by default may well
make sense anyway.)

Thanks!

-- 
====================================
Ian Pilcher                                         arequipeno@gmail.com
Sometimes there's nothing left to do but crash and burn...or die trying.
====================================


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Re: [lm-sensors] it87.fix_pwm_polarity

[Ian Pilcher]

On 08/12/2013 09:54 AM, Ian Pilcher wrote:
> I am setting up a Thecus N5550 NAS, and I found that the it87 driver
> disables PWM control of the drive bay fan (it87.656/pwm3) unless I pass
> the fix_pwm_polarity parameter.  Once I add that parameter, fan control
> appears to work just fine.
> 
> Does this setting actually invert the voltage that is supplied to the
> fan?  If so, does this have the potential to damage the fan itself (or
> other components)?

Anyone?

-- 
====================================
Ian Pilcher                                         arequipeno@gmail.com
Sometimes there's nothing left to do but crash and burn...or die trying.
====================================


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Re: [lm-sensors] it87.fix_pwm_polarity

[Guenter Roeck]

On Fri, Aug 16, 2013 at 11:34:49AM -0500, Ian Pilcher wrote:
> On 08/12/2013 09:54 AM, Ian Pilcher wrote:
> > I am setting up a Thecus N5550 NAS, and I found that the it87 driver
> > disables PWM control of the drive bay fan (it87.656/pwm3) unless I pass
> > the fix_pwm_polarity parameter.  Once I add that parameter, fan control
> > appears to work just fine.
> > 
> > Does this setting actually invert the voltage that is supplied to the
> > fan?  If so, does this have the potential to damage the fan itself (or
> > other components)?
> 
> Anyone?
> 
It just changes the pwm polarity from active low to active high unless
fan control is set to automatic mode. That doesn't damage anything.

Does automatic fan control for the drive bay fan work if you don't load
the driver ? Also, what kernel log message do you get when you load the
driver with or without the parameter ?

Thanks,
Guenter

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Re: [lm-sensors] it87.fix_pwm_polarity

[Ian Pilcher]

On 08/16/2013 01:57 PM, Guenter Roeck wrote:
> It just changes the pwm polarity from active low to active high unless
> fan control is set to automatic mode. That doesn't damage anything.

Good to know.

> Does automatic fan control for the drive bay fan work if you don't load
> the driver ? Also, what kernel log message do you get when you load the
> driver with or without the parameter ?

I don't believe so.  Without the module loaded the fan seems to always
run at about 75% of its maximum speed.

It is hard to be 100% sure, because the temperatures reported by the
IT8728F don't seem to ever vary by more than a few degrees, even when
coretemp reports significant changes (around 20 degrees).  So it's
possible that automatic fan control is "working," but getting garbage
input.

If I load the module after a cold-boot without the parameter, I get:

  it87 it87.656: Detected broken BIOS defaults, disabling PWM interface

Once I've loaded it with the fix_pwm_polarity=1 one time, I can unload/
reload the module without any special parameters, and PWM continues to
work.  IIRC, this is true across warm reboots.

Note that bad/incomplete setup by the BIOS appears to be somewhat common
on this hardware.  This is a Thecus N5550 NAS, and the manufacturer
expects people to run their Linux-based "firmware."  Their add-on kernel
modules do some setup work (configuring ICH GPIOs) which would normally
be done by the BIOS.

HTH

-- 
====================================
Ian Pilcher                                         arequipeno@gmail.com
Sometimes there's nothing left to do but crash and burn...or die trying.
====================================

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Re: [lm-sensors] it87.fix_pwm_polarity

[Guenter Roeck]

On Fri, Aug 16, 2013 at 02:28:14PM -0500, Ian Pilcher wrote:
> On 08/16/2013 01:57 PM, Guenter Roeck wrote:
> > It just changes the pwm polarity from active low to active high unless
> > fan control is set to automatic mode. That doesn't damage anything.
> 
> Good to know.
> 
> > Does automatic fan control for the drive bay fan work if you don't load
> > the driver ? Also, what kernel log message do you get when you load the
> > driver with or without the parameter ?
> 
> I don't believe so.  Without the module loaded the fan seems to always
> run at about 75% of its maximum speed.
> 
> It is hard to be 100% sure, because the temperatures reported by the
> IT8728F don't seem to ever vary by more than a few degrees, even when
> coretemp reports significant changes (around 20 degrees).  So it's
> possible that automatic fan control is "working," but getting garbage
> input.
> 
> If I load the module after a cold-boot without the parameter, I get:
> 
>   it87 it87.656: Detected broken BIOS defaults, disabling PWM interface
> 
> Once I've loaded it with the fix_pwm_polarity=1 one time, I can unload/
> reload the module without any special parameters, and PWM continues to
> work.  IIRC, this is true across warm reboots.
> 
In that case the driver does exactly what it is supposed to do.
It detects that the pwm configuration is broken and disables it.
With the parameter, it tries to correctly configure and enable it instead. 

Guenter

> Note that bad/incomplete setup by the BIOS appears to be somewhat common
> on this hardware.  This is a Thecus N5550 NAS, and the manufacturer
> expects people to run their Linux-based "firmware."  Their add-on kernel
> modules do some setup work (configuring ICH GPIOs) which would normally
> be done by the BIOS.
> 
> HTH
> 
> -- 
> ====================================
> Ian Pilcher                                         arequipeno@gmail.com
> Sometimes there's nothing left to do but crash and burn...or die trying.
> ====================================
> 

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