On Wed, 11 Aug 2004, Mark M. Hoffman wrote:
> Hi Jean:
>
> * Jean Delvare <khali at linux-fr.org> [2004-08-11 22:26:16 +0200]:
> > > I think these should be named e.g. pwm1_auto_channels to make clear
> > > the distinction between a tacho input (fanX) and a pwm output (pwmX).
> > >
> > > (/me goes off to look at 2.6 sysfs_interface doc again)
> > >
> > > Oh dear. I'm sorry I wasn't paying attention to this sooner, but I
> > > think our interface needs revision again. All of the fan[nr]_pwm*
> > > files should really just be pwm[nr]*.
> > >
> > > The association between tacho input and pwm output is arbitrary and
> > > depends on mainboard maker. E.g. our script prog/pwm/pwmconfig is
> > > made to discover the relationships.
> > >
> > > Would anyone object to such a patch for 2.6 kernel drivers?
> >
> > I wish someone noticed that *before* I did the change the other way
> > around back in version 2.6.5...
> >
> > I'm not sure I agree with you. Old chips clearly had PWM outputs and
> > tachometers unlinked, but newer chips (Analog ADM1031, SMSC LPC47M1xx,
> > National PC8736x) clearly assume that pwmN and fanN refer to the same
> > physical fan. Of course, some motherboard manufacturers will ignore that
> > recommendation, but they are to blame. For example, the SMSC LPC47M1xx
> > chips will stop monitoring fan1 when pwm1 is enabled and has a duty
> > cycle of 0%. Thus the driver has to force fan1 to 0 in this case. If the
> > manufacturer used fan1 and pwm1 for different fans, then the monitored
> > fan cannot be monitored anymore when the controlled fan is turned off.
> >
> > Are there examples of recent chips which obviously don't consider that
> > pwmN and fanN are linked? For example chips having a different count of
> > tachometers and PWM outputs?
>
> Yeah, LM93... four tachos, two PWM outputs. Odd, but it seems like one
> anticipated configuration is to drive fans 1-2 (tacho's 1-2) *both*
> from pwm1. I could be wrong about that though.
>
Your not. A real pending configuration looks like:
Fan A1----\
Fan A2----|---\
>-------PWM1
Fan B1----|---/
Fan B2----/
Fan C1----|------------PWM2
Fan C2----/
Cheers...james
<snip>
