linux-kernel - Re: [PATCH v3] hwmon: (k10temp) Enable AMD3255 Proc to show negative temperature

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Message-ID: <88525fc7-ee7b-969a-cb14-02ca8736f229@roeck-us.net>
Date:   Mon, 19 Jun 2023 13:40:28 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Limonciello, Mario" <mario.limonciello@....com>,
        Baskaran Kannan <Baski.Kannan@....com>, babu.moger@....com,
        clemens@...isch.de, jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] hwmon: (k10temp) Enable AMD3255 Proc to show negative
 temperature

On 6/19/23 12:58, Limonciello, Mario wrote:
> 
> On 6/19/2023 2:48 PM, Guenter Roeck wrote:
>> On 6/19/23 11:53, Limonciello, Mario wrote:
>> [ ,,, ]
>>
>>> So Pinnacle Ridge and Summit Ridge (Zen/Zen+) have model_id_str values of 'B1' and 'B2'.
>>> I think we should be able to detect those and only avoid showing the negative values when:
>>>
>>> * Family 17h
>>> * Model > 0x00
>>> * Model <= 0x0f
>>> * Model ID str B1 or B2
>>>
>>
>> Threadripper 1950X model string is "AMD Ryzen Threadripper 1950X 16-Core Processor".
>> Not sure where B1 or B2 is seen, but it is not in the model string.
>>
>> Guenter
>>
> Sorry; I thought you were talking about desktop parts and didn't realize it was a Threadripper
> part that prompted all of this.
> 
> I looked at the old commit aef17ca127, and it seems that this is tied to the usage of some
> overclocking knobs offered by some BIOS vendors.
> 

Correct.

> As an idea to avoid the initial issue and all these hacks; what about changing the logic to
> compare the calculated temperature against the max temperature?  If it's greater than the max
> THEN set it to zero.
> 

No, that won't work anymore. In the old code, negative temperatures were displayed as large
positive temperatures. This was changed later, and temperatures are now reported as
negative temperatures.

Is there a way to detect if those overclocking knobs are set ? Alternatively, we could\
possibly just check if the CPU is a Threadripper and limit the hack to Threadripper CPUs.

Thanks,
Guenter