[PATCH v8 10/13] hwmon: peci: Add cputemp driver

[Winiarska, Iwona]

On Mon, 2023-03-20 at 14:45 +0300, Paul Fertser wrote:
> Hello,
> 
> We are seeing wrong DTS temperatures on at least "Intel(R) Xeon(R)
> Bronze 3204 CPU @ 1.90GHz" and most probably other Skylake Xeon CPUs
> are also affected, see inline.
> 
> On Tue, Feb 08, 2022 at 04:36:36PM +0100, Iwona Winiarska wrote:
> > Add peci-cputemp driver for Digital Thermal Sensor (DTS) thermal
> > readings of the processor package and processor cores that are
> > accessible via the PECI interface.
> ...
> > +static const struct cpu_info cpu_hsx = {
> > +       .reg            = &resolved_cores_reg_hsx,
> > +       .min_peci_revision = 0x33,
> > +       .thermal_margin_to_millidegree =
> > &dts_eight_dot_eight_to_millidegree,
> > +};
> > +
> > +static const struct cpu_info cpu_icx = {
> > +       .reg            = &resolved_cores_reg_icx,
> > +       .min_peci_revision = 0x40,
> > +       .thermal_margin_to_millidegree = &dts_ten_dot_six_to_millidegree,
> > +};
> ...
> > +       {
> > +               .name = "peci_cpu.cputemp.skx",
> > +               .driver_data = (kernel_ulong_t)&cpu_hsx,
> > +       },
> 
> With this configuration we get this data:
> 
> /sys/bus/peci/devices/0-30/peci_cpu.cputemp.skx.48/hwmon/hwmon15# grep .
> temp[123]_{label,input}
> temp1_label:Die
> temp2_label:DTS
> temp3_label:Tcontrol
> temp1_input:30938
> temp2_input:67735
> temp3_input:80000
> 
> On the host system "sensors" report
> 
> Package id 0:  +31.C (high = +80.C, crit = +90.C)
> 
> So I conclude Die temperature as retrieved over PECI is correct while
> DTS is mis-calculated. The old downstream code in OpenBMC was using
> ten_dot_six_to_millidegree() function for conversion, and that was
> providing expected results. And indeed if we reverse the calculation
> here we get 80000 - ((80000-67735) * 256 / 64) = 30940 which matches
> expectations.
> 

Hi!

Thanks for the report.

It was changed between v2 and v3 after a report about negative temperature on
pre-ICX platforms:
https://lore.kernel.org/lkml/6891496eabcc6f9cacec4fea505fb757ea9c11fc.camel@intel.com/

Unfortunately, I'm not able to test this on Cascade Lake X (or any other pre-ICX
platform).
I just sent a patch that changes SKX to use S10.6 format:
https://lore.kernel.org/lkml/20230321090410.866766-1-iwona.winiarska@intel.com/

Thanks
-Iwona