linux-kernel - Re: [PATCH v2 3/4] hwmon: smpro: Add Ampere's Altra smpro-hwmon driver

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Message-ID: <d9ef40ea-e4ee-cea8-96df-90ffabdff53c@roeck-us.net>
Date:   Wed, 7 Apr 2021 05:11:49 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Quan Nguyen <quan@...amperecomputing.com>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Jean Delvare <jdelvare@...e.com>,
        Rob Herring <robh+dt@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Jonathan Corbet <corbet@....net>, linux-hwmon@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-aspeed@...ts.ozlabs.org,
        openbmc@...ts.ozlabs.org
Cc:     Open Source Submission <patches@...erecomputing.com>,
        Phong Vo <phong@...amperecomputing.com>,
        "Thang Q . Nguyen" <thang@...amperecomputing.com>
Subject: Re: [PATCH v2 3/4] hwmon: smpro: Add Ampere's Altra smpro-hwmon
 driver

On 4/7/21 12:41 AM, Quan Nguyen wrote:
[ ... ]
>>
>> But then why don't you just use reg_ext to store SOC_VR_HOT_THRESHOLD_REG
>> or MEM_HOT_THRESHOLD_REG ? It is already available, after all, and with it
>> the code could be simplified to
>>
>>         ret = regmap_read(hwmon->regmap, temperature[channel].reg_ext, &value);
>>         if (ret)
>>             return ret;
>>
> Thank you for the comment.
> 
> Will change code follow this suggestion, will include in next version
> 
>> I don't have a datasheet, but I do wonder what is in bit 9..15. Any idea ?
>> Main question is if there is a sign bit, as theoretic as it may be.
>>
> The original intention was to use this as 9-bit 2-complement value follow LM75, but the fact is that the operation temperature is 0-125 C degree, so we simply use it as-is.
> 

The operational temperature is not the question here. The question is if the
chip _reports_ a sign. If it does, it should be handled, even if it is outside
the operational range. The reported range is relevant here, not the operational
range. After all, the chip won't really blow apart at -1 degrees C.

Thanks,
Guenter