On 9/14/21 10:11 AM, Oskar Senft wrote:

Hi Guenter

quoted

quoted

Following the example from tmp421, this could then be like this:

Something like that, only we'll need something to distinguish
temperature sensors from other sensor types, eg voltage or current.
Maybe a "type" property. I'd suggest "sensor-type", but we have
non-sensor attributes such as fan count and pwm values which should
be covered as well. But it looks like a good start for a set of
generic sensor properties.

Would it be acceptable to simply number the sensors and document which
sensor has which number?

Something like this:
0 = LTD
1 = RTD1
2 = RTD2
3 = RTD3
4 = FAN1
5 = FAN2
6 = FAN3

That might be a possibility, though it would have to be well defined
for each chip (nct7802 also has voltage sensors). We'll have to discuss
this with Rob.

Personally I think I would prefer using a type qualifier - that seems
cleaner. But that is really a matter of opinion.

Would we also want to be able to define PWMs? From what I can tell the
driver does not support running individual pins in GPIO mode, right?
So I'm not quite clear what "disabling PWM" would actually mean.

The ABI states that fans should run at full speed in that case,
though that may be chip dependent (some chips stop the fan if pwm
control is turned off).

Anyway, if we simply go by "sensor number", that would mean that we'd
have different attributes depending on the sensor number. Would that
be ok?

That is a question for Rob to answer.

Also, I'm sorry, I think I just realized that in "voltage mode" we
don't seem to get a temperature reading. I hadn't actually looked
through more of the datasheet except for the single MODE register
before. But I don't think this makes a difference for what I proposed
so far?

We don't ? I thought this reflects temperature measurement with a
transistor instead of a diode (which would be current based).
Hard to say - the datasheet is a bit vague in that regard.

quoted

quoted

         /* LTD */
         input@0 {
             reg = <0x0>;
             status = "okay";

Not sure what the default is here ('okay' or 'disabled').
We'd also need to define what to do if there is no data
for a given sensor.

I think I'd like to keep previous behavior unmodified. From what I can
tell previous behavior was:
- xTDs enabled by default
- RTD modes unmodified, i.e. defaulting to whatever the HW comes up with

The NCT7802Y can self-program from an EEPROM, so I assume we should
honor the "power-up configuration" obtained from there? I.e. if no
configuration is provided in the device tree, the driver should use
whatever configuration the chip has when the driver is loaded.

Definitely yes. My question was more what to do if the information
in devicetree nodes is incomplete.

Thanks,
Guenter

quoted

quoted

             label = "voltage mode";

That isn't the idea for "label", as "label" would be expected to
show up as tempX_label (and a label of "voltage mode" would be odd).
The label should indicate where the sensor is located on a board,
such as "inlet" or "outlet".

Yes, absolutely. This was a bad example on my part. In my
understanding "label" is just a string that we pass through.

Oskar.