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Subject: Re: [PATCH v2 3/4] hwmon: smpro: Add Ampere's Altra smpro-hwmon driver
To: Quan Nguyen <quan@os.amperecomputing.com>, Joel Stanley <joel@jms.id.au>, 
 Andrew Jeffery <andrew@aj.id.au>, Jean Delvare <jdelvare@suse.com>,
 Rob Herring <robh+dt@kernel.org>, Lee Jones <lee.jones@linaro.org>,
 Jonathan Corbet <corbet@lwn.net>, linux-hwmon@vger.kernel.org,
 devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-doc@vger.kernel.org, linux-aspeed@lists.ozlabs.org,
 openbmc@lists.ozlabs.org
References: <20210329015238.19474-1-quan@os.amperecomputing.com>
 <20210329015238.19474-4-quan@os.amperecomputing.com>
 <bac92db0-3ef6-1615-0e92-aabd54fd0580@roeck-us.net>
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From: Guenter Roeck <linux@roeck-us.net>
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Cc: Open Source Submission <patches@amperecomputing.com>,
 "Thang Q . Nguyen" <thang@os.amperecomputing.com>,
 Phong Vo <phong@os.amperecomputing.com>
Errors-To: openbmc-bounces+openbmc=archiver.kernel.org@lists.ozlabs.org
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 <openbmc-bounces+openbmc=archiver.kernel.org@lists.ozlabs.org>

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