Re: [lm-sensors] [RFC PATCH] Allow the configuration register to be

[Jean Delvare <khali@linux-fr.org>]

On Mon, 13 Sep 2010 11:09:06 -0700, Guenter Roeck wrote:
> On Mon, Sep 13, 2010 at 01:41:21PM -0400, Jean Delvare wrote:
> > On Mon, 13 Sep 2010 09:51:09 -0700, Guenter Roeck wrote:
> > > I found the following attributes used for the update inverval.
> > > 
> > > adt7470.c	auto_update_interval
> > > lm95241.c	rate
> > > adm1031.c	update_rate
> > > 
> > > Not sure about adt7470.c, ince it reflects an automatic interval, but would it make sense
> > > to update lm95241.c to use the standard attribute ?
> > 
> > Yes it would.
> > 
> > > On a side note, update_rate (or rate) doesn't really reflect its use. A "rate"
> > > would be measured in updates/time, not in absolute time. Or, in other words,
> > > it reflects a frequency, not an interval. So we are really talking about intervals.
> > > Not sure if that is worth bitching about, but since the attribute is quite new
> > > it might make sense to think about it.
> > 
> > Jonathan Cameron (Cc'd) had a similar concern:
> > http://lists.lm-sensors.org/pipermail/lm-sensors/2010-May/028596.html
> > 
> > Nobody seemed to care back then. I can't disagree with both of you, but
> > OTOH I don't feel too strongly about it either. So if someone submits a
> > patch making things better, that's fine with me, but I won't spend my
> > own time on it.
>
> I'll submit a set of patches. update_interval ok ? It reflects the time between
> events, while period tends to reflect a duration.

Yes, I would be fine with update_interval. Jonathan, OK with you too?

> > > Resolution would have to be sensor dependent, since each sensor can have its own resolution.
> > > Would be nice to have an attribute for that.
> > 
> > Not too sure about that. I had the same reaction at first, but do we
> > actually know of devices where the resolution isn't global?
>
> Yes, in the lm90 driver. Only max6657/58/59 and max6646 have extended local
> temperatures, all other chips have only 8 bit resolution for the local temperature.
> Remote temperatures are all extended, ie have higher resoution.

But resolution can't be changed on these chips, can it? I think the
main purpose of these files is to let the user change the resolution
for chips which support this (usually this is an update speed /
resolution trade-off). Or do you believe that having read-only
attributes exposing fixed resolutions would be valuable?

I'm a little worried because resolution as a bit number isn't too
informative and doesn't quite work as a device-independent value. If
you really want the information to be exposed to user-space for all
devices, then we'd rather use actual sensor units (mV, m°C, whatever)
for resolution, and possibly add other attributes for the range. But
this means adding a whole lot of attribute files for some devices (if
we do it on a per-channel basis), so we first have to determine whether
it is really worth it. I don't think it is, but you can try and
convince me.

-- 
Jean Delvare

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