Re: Weird Dell SMM bug since 6.18

["Guy Boldon" <gb@guyboldon.com>]

Hi Guenter,

Thank you for the explanations, much appreciated. 


On Thu Mar 19, 2026 at 4:52 PM CET, Guenter Roeck wrote:
> The use of -ENODATA in hwmon to report that a value is not available is
> relatively new and isn't even fully documented in the sysfs ABI (admittedly
> a major oversight). The major driver for its use is that it more accurately
> reflects reality as reported by the "sensors" command if an attribute value
> is not available (sensors reports "N/A" instead of an error message if it
> gets an -ENODATA error).

Ah, it seemed somewhat new and that makes sense. -ENODATA converts to
a clean N/A without an error message. We will adjust to handle -ENODATA 
going forward.

>> As a related point: gpd_fan returns -EOPNOTSUPP rather than -ENODATA
>> when in auto mode, and documents that behavior in the kernel docs. The
>
> Please feel free to submit a patch to fix that.

I'll submit a patch for that.

> The best we can do is to find a means to improve consistency, but as you
> can see here even that is difficult because different people will have
> different opinions on how that consistency should look like. Error response
> will vary, as will attribute visibility.
>
> If you would like to get actively involved, please feel free to submit patches
> improving the documentation (Documentation/hwmon/sysfs-interface.rst,
> Documentation/ABI/testing/sysfs-class-hwmon, and or driver specific
> documentation) as well as driver patches to help improve consistency across
> drivers.

I agree and I would like to help improve consistency for the interface. I'll
look at the docs as well. CoolerControl is a direct consumer of this interface
across a large range of drivers, but improving consistency, I think, benefits 
anyone interacting with more than a handful of drivers.

Thanks again,
Guy