Re: hwmon (nct6775): Please fix Invalid temperature source error for NCT6798D

[Alexey Galakhov <agalakhov@gmail.com>]

Hi,

I'm facing the same problem. I did some research on my machine.

On Fri, 2020-07-03 at 10:10 -0700, Guenter Roeck wrote:

> There is nothing much if anything we can do about that. The NCT6798D
> datasheet reports temperature source 28 as reserved. You could ask
> Asus for support, but their usual response is that they don't support
> Linux.

Looks like there are different versions of the datasheet. The one of
NCT6796D, Revision 0.6 states that 28 (0x1c or 11100) is "Select PECI
Agent 0 Calibration as CPUFAN monitoring source." This seems to be correct
since the fan in question is the CPU one and the value of "PECI Agent 0
Calibration" is actually very similar to the CPU temperature and rises
with CPU load.

Also, looking at the driver code I found no signs of reading so-called
"HM Read-Only Registers". They are described in section 9.481 of the
above datasheet. They are I/O ports (readable with `inb`) with their
base address located in configuration registers 0x64 and 0x65 of the
SuperIO. Some temperatures seem to be directly readable only through
these registers. Looks like the driver monitors all temperatures only
indirectly via switchable channels, is it true?

Regards,
Alexey