linux-kernel - Re: [PATCH v8 10/13] hwmon: peci: Add cputemp driver

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Date:   Mon, 20 Mar 2023 14:45:15 +0300
From:   Paul Fertser <fercerpav@...il.com>
To:     Iwona Winiarska <iwona.winiarska@...el.com>
Cc:     linux-kernel@...r.kernel.org, openbmc@...ts.ozlabs.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-aspeed@...ts.ozlabs.org, linux-doc@...r.kernel.org,
        Dave Hansen <dave.hansen@...el.com>,
        Zev Weiss <zweiss@...inix.com>,
        Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Guenter Roeck <linux@...ck-us.net>, devicetree@...r.kernel.org,
        Jean Delvare <jdelvare@...e.com>,
        Arnd Bergmann <arnd@...db.de>,
        Billy Tsai <billy_tsai@...eedtech.com>,
        Rob Herring <robh+dt@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-arm-kernel@...ts.infradead.org, linux-hwmon@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>,
        Andrew Jeffery <andrew@...id.au>,
        Randy Dunlap <rdunlap@...radead.org>,
        Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v8 10/13] hwmon: peci: Add cputemp driver

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.

-- 
Be free, use free (http://www.gnu.org/philosophy/free-sw.html) software!
mailto:fercerpav@...il.com