Quoting Jean Delvare <khali at linux-fr.org>:
> > > In the LM85/ADM1027 driver it's called pwm1_zone.
> > >
> > > It has the values:
> > > -1: PWM disabled, fan at 100%
> > > -2: PWM under manual control ('pwm1' or 'pwm1_value' is
> > > writable)
> > > 1: PWM is controlled by temp1_input
> > > 2: PWM is controlled by temp2_input
> > > 123: PWM is controlled by max value of all three
> > > 0: PWM disabled, fan at 0%
> > >
> > > The other parameters have equivalents in the lm85 driver as well.
> > >
> > > zone#_limit (fan "turn on" temperature (1*))
> > > zone#_hyst (range below limit fan remains on. Fixed at 5 deg
> > in
> > > this chip?)
> > > zone#_range (temperature range (2*))
> > > pwm#_min (PWM value at low limit. (4*))
> > >
> > > :v)
> >
> > Seems to be a good approach, and it has the advantage of already
> > beeing implemented on some drivers.
>
> I think that the lm85 driver is actually the only one to do that. Since
> it isn't standardized yet, I have to say I do not consider much benefit
> in following what was done. Not that I denigrate Philip's work, nor
> does it mean that I dislike his approach. All I mean is that if it
> happens that this doesn't cover the other chips correctly, or doesn't
> fit in the "file names are self-descriptive" rule, we better change
> what exists in the name of uniformity.
>
> > Jean, what do you think about that ?
>
> First of all I have to say that I completely ignored that one driver
> already has auto fan speed support. Thanks Philip for joining the
> conversation and providing some insight about how you did implement it
> on your side.
>
> Here are the drawbacks I see at first sight:
>
> 1* pwm1_zone == -1 is what other drivers implement with pwm1_enable ==
> 0. I would like to avoid having two ways to express the same thing if
> possible. OTOH, one will wonder what happens if a user sets pwm1_enable
> == 0 and pwm1_auto at the same time. I don't really know and think that
> it'll probably depend on chip's implementation (depends if there are
> two separate bits in the chip, or one three-state value).
>
> Likewise, pwm1_zone == 0 is (more or less) pwm_enable == 1 && pwm1 ==
> 0,
> and pwm1_zone == -1 is pwm_enable == 1.
>
> I think we better stick to the one file - one value (i.e. one meaning)
> philosophy. Philip, I guess that the idea of setting these different
> things in a single value were inspired by the way the LM85 implements
> it?
>
> 2* About the range: the same way we decided that hysteresis values
> should be expressed as absolute temperatures and not a difference
> relative to another limits, I think we should express the max temp (for
> auto fan control) as an absolute value and not a range from the min
> temp. The fact that some (most?) chips use a range is obviously made so
> as to spare a few bits in the registers. The userspace doesn't care
> about these implementation details.
>
> 3* I was thinking that what is named pwm1_zone in lm85 could be a
> bitfield. Each bit links the corresponding temperature channel to this
> PWM. That way we are sure we can extend the values in a consistent way
> if a later chip has more than 3 temperature channels, and if it allows
> to link more than one, but less than all, channels to a given PWM.
>
> Anyway, this proves that we *really* need to discuss a bit more about a
> common interface to this functionality. I will try to read as much as
> possible about the various implementations (IT87, LM85, ADM1030 and
> W836x7) before the end of the week so as to make sure that I understand
> how things do work. I invite each of you to do the same so that our
> discussion is as constructive as possible.
I'll do the same.
>
> Thanks a lot.
>
> --
> Jean Delvare
> http://www.ensicaen.ismra.fr/~delvare/
>
>
--
-------------------------------------------------
Alexandre d'ALTON
alex at alexdalton.org
