[lm-sensors] [RFC PATCH 0/3] Support for all SHT15 features

Guenter Roeck guenter.roeck at ericsson.com
Thu Mar 17 22:14:45 CET 2011

On Thu, 2011-03-17 at 16:02 -0400, Vivien Didelot wrote:
> Thanks for your comments Guenter,
> > Two questions:
> > - Which of the new attributes are really expected to change during
> >   runtime ?
> >   If an attribute is not expected to change during runtime, it should be
> >   configured statically (eg with platform data or device tree), and not
> >   with a sysfs attribute.
> The battery_alarm and heater_enable attributes are expected to
> change during runtime. The heater should not be enabled all the time, it
> just needs to be set for a short period for validation purposes (e.g.
> cross-validating the dew point calculation). And of course, the battery
> fault alarm is important, as measurements become invalid if the sensor's
> power source falls below 2.47 V (not all platforms have power regulators).
Yes, but one thought here would be that the alarm should be tied to the
core attribute, ie be "humidity1_alarm", instead of using a new
non-standard attribute name - especially if its impact is that
measurements become invalid as a result. The exact meaning of the
warning could then be clarified in the documentation.

> The ability to switch resolution will mainly impact transfer speeds and
> power consumption, depending on the sensor. It makes sense to use the
> number of bits rather than keywords or predefined codes as they will most
> probably be different with each manufacturer.
> Wether it might be a runtime attribute or not, I guess, will depend on the
> ability to change the resolution depending on the power profile on mobile
> platforms. Would it be insightful?
> > - For any remaining attributes, does they really add value ?
> >   If they adds value, it may add value for other drivers as well and may
> >   warrant an ABI extension. If so, that should be discussed.
> The checksumming attribute adds value in my opinion as not all sensors are
> closely tied to the platform itself, and thus might suffer from data
> corruption. Other devices supporting that feature will benefit from that.
> We chose the "checksumming" attribute name based on the only example of
> similar attribute found in drivers/s390/net/qeth_l3_sys.c.
> I think the name is quite explicit for the feature.
The name is inconsistent with heater_enable and other (standard)
xxx_enable hwmon attributes.

> The last feature, OTP reload, is very device-specific and allows saving
> 10ms for each measurement while loosing on precision. Here again, power
> consumption will be affected.
The notion of using device specific attributes to control power
consumption sounds scary and not very scalable to me. Hard to imagine
that power management depending on such attributes would ever work.

The driver doesn't support the existing PM infrastructure at all. If
power management/control is of concern, it might make more sense to add
support for the power management infrastructure instead of adding
non-standard attributes to accomplish the same goal.


> > 
> > Either case, I would expect attributes to be documented. If that means
> > that driver documentation needs to be added in the first place because
> > it does not exist - maybe that should be first priority anyway before
> > adding new functionality to a driver.
> I think that checksumming and resolution should become part of the
> documentation. Do you see any impediment?
> Concerning device-specific attributes, should their naming be normalized?
> e.g. by prefixing the attribute name with the device driver name or
> similar? In either case, I will add documentation to the patch.
> Regards,
> Vivien.

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