linux-kernel - Re: [PATCHv1] hwmon: adm9240: handle temperature readings below 0

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Date:   Tue, 4 Oct 2016 21:09:10 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     "jdelvare@...e.com" <jdelvare@...e.com>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Wang <Michael.Wang@...iedtelesis.co.nz>
Subject: Re: [PATCHv1] hwmon: adm9240: handle temperature readings below 0

On 10/05/2016 09:54 AM, Guenter Roeck wrote:
> On Tue, Oct 04, 2016 at 05:08:00PM +1300, Chris Packham wrote:
>> Unlike the temperature thresholds the temperature data is a 9-bit signed
>> value. This allows and additional 0.5 degrees of precision on the
>> reading but means we can't rely on sign-extension to handle negative
>> values.
>>
>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
>> ---
>>  drivers/hwmon/adm9240.c | 19 +++++++++++++++++--
>>  1 file changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/hwmon/adm9240.c b/drivers/hwmon/adm9240.c
>> index 98114ce..6929b25 100644
>> --- a/drivers/hwmon/adm9240.c
>> +++ b/drivers/hwmon/adm9240.c
>> @@ -107,6 +107,21 @@ static inline s8 TEMP_TO_REG(long val)
>>  	return clamp_val(SCALE(val, 1, 1000), -40, 127);
>>  }
>>
>> +/* 8-bit signed temperature (from Thigh, Tlow etc) */
>> +static inline int TEMP_FROM_REG(s8 val)
>> +{
>> +	return val * 1000;
>> +}
>
> This does not any value; please drop.
>

My intention was to make the code handling the 8-bit temperature 
thresholds look the same as that handling the 9-bit temperature reading. 
A moot point if we're moving in a new direction.

>> +
>> +/* 9-bit signed temperature (from temperature data) */
>> +static inline int TEMP_FROM_DATA_REG(s16 val)
>
> Please don't use uppercase for functions.
>

Noted. I was following suit with the existing TEMP_TO_REG above.

>> +{
>> +	if (val > 255)
>> +		val -= 512;
>> +
>> +	return val * 500;
>
> At the surface, this is identical to
> 	return sign_extend(val, 9) * 500;

I didn't know sign_extend() existed, thanks for pointing it out.

> However, the real problem is around line 200, where the sign extension is
> attempted but fails. It would be better to drop the '/ 128'
> there and simplify the above code to
>
> 	return val / 128 * 500;
>
> With that, it might be better to just drop the new function and move the
> expression into the calling code.

I'll give that a go and send a v2.

>
> Of course, all that doesn't solve the real problem in this driver, which is
> that it ignores error codes from the smbus functions, but that is a different
> problem.

Yeah I'd noted that too. This patch is actually a port of changes we've 
made to a custom LM81 driver based on the original adm9240 driver which 
included some error handling. I'll look at bringing more of that code in 
for a future patch.

>
> Thanks,
> Guenter
>
>> +}
>> +
>>  /* two fans, each with low fan speed limit */
>>  static inline unsigned int FAN_FROM_REG(u8 reg, u8 div)
>>  {
>> @@ -263,7 +278,7 @@ static ssize_t show_temp(struct device *dev, struct device_attribute *dummy,
>>  		char *buf)
>>  {
>>  	struct adm9240_data *data = adm9240_update_device(dev);
>> -	return sprintf(buf, "%d\n", data->temp * 500); /* 9-bit value */
>> +	return sprintf(buf, "%d\n", TEMP_FROM_DATA_REG(data->temp));
>>  }
>>
>>  static ssize_t show_max(struct device *dev, struct device_attribute *devattr,
>> @@ -271,7 +286,7 @@ static ssize_t show_max(struct device *dev, struct device_attribute *devattr,
>>  {
>>  	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
>>  	struct adm9240_data *data = adm9240_update_device(dev);
>> -	return sprintf(buf, "%d\n", data->temp_max[attr->index] * 1000);
>> +	return sprintf(buf, "%d\n", TEMP_FROM_REG(data->temp_max[attr->index]));
>>  }
>>
>>  static ssize_t set_max(struct device *dev, struct device_attribute *devattr,
>> --
>> 2.10.0
>>
>> --
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>