Re: [lm-sensors] Need some guidance on adhering to the sysfs

["Mark M. Hoffman" <mhoffman@lightlink.com>]

Hi guys:

> On Thu, 19 Apr 2007 12:04:28 -0700, Juerg Haefliger wrote:
> > I'm struggling with the same issue for the DME1737 I'm currently
> > working on. This chip also features temp zones and "hottest of x,y,z"
> > PWM control. The current sysfs standard is not flexible enough to
> > handle these features, especially the combination of a single PWM
> > being controlled by multiple temp inputs and multiple PMWs being
> > controlled by the same temp input. I believe we need another layer of
> > mapping. I.e. temp->pwm is not sufficient, but rather temp->zone->pwm.
> > 
> > I therefore propose the add the following sysfs attributes to our standard:
> > 
> > zone[1-*]_auto_channels_temp   for temp-to-zone mapping
> > pwm[1-*]_auto_channels_zone   for zone-to-pwm mapping
> > zone[1-*]_auto_point[1-*]_temp   for zone temp auto points.

* Jean Delvare <khali@linux-fr.org> [2007-04-22 17:29:04 +0200]:
> I don't see what value it adds compared to what we currently have.
> 
> We have pwm[1-*]_auto_channels_temp, which is a bit vector. We have one
> file per PWM, one bit per temperature channel, so all in all we have a
> Npwm x Ntemp matrix, or N-N relation between PWM and temperatures. This
> already allows us to handle cases such as "the hottest of tempA and
> tempB control pwmC" or "tempD controls pwmE and pwmF".
> 
> You propose to add the concept of zone. According to the above, each
> zone could include any temperature channel, so we have a N-N relation
> between zones and temperatures. Then you express another N-N relation
> between PWM channels and zones. As far as I can see, this results in a
> N-N relation between temperatures and PWM, just expressed differently.
> Am I missing something? What do you think it would let us express,
> which the current model doesn't?

I was never a big fan of the pwm_auto standard interface in the first place.
IMHO, the various chips implement automatic fan control in so many different
ways that the abstraction is bound to be mis-aligned for most chips, no matter
how we model it.

Or if not, then the abstraction would necessarily have so many options that it
hardly even counts as an abstraction.

I don't see it in Documentation/hwmon/sysfs-interface, but IIRC it was agreed
that the pwm_auto standard interface was optional.  So, a driver may support
that interface as best it can, OR it can support one which describes its actual
capabilities precisely (so long as there is no collision of sysfs names).  It
is important to note that libsensors has no pwm_auto support anyway, and none
is planned.

So I agree with Jean that we shouldn't extend the "standard" interface.  If
you feel that the standard interface is insufficient for your hardware, then
go ahead and create something completely different.  If the chip is "close"
to fitting the standard interface, I would prefer you support that as best
you can.

Regards,

-- 
Mark M. Hoffman
mhoffman@lightlink.com


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