linux-kernel - Re: [PATCH v1 2/2] iio: temperature: add driver support for ti tmp117

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Date:   Sun, 21 Mar 2021 06:23:08 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Puranjay Mohan <puranjay12@...il.com>,
        alexandru.ardelean@...log.com, jic23@...nel.org,
        devicetree@...r.kernel.org, knaack.h@....de,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] iio: temperature: add driver support for ti tmp117

On 3/21/21 6:07 AM, Lars-Peter Clausen wrote:
> On 3/20/21 7:45 AM, Puranjay Mohan wrote:
>> TMP117 is a Digital temperature sensor with integrated NV memory.
>>
>> Add support for tmp117 driver in iio subsystem.
>>
>> Datasheet:-https://www.ti.com/lit/gpn/tmp117
>>
>> Signed-off-by: Puranjay Mohan <puranjay12@...il.com>
>
> This looks good to me. Just two small bits I overlooked during the 
> first review, sorry for that.
>
>> +};
>> +
>> [...]
>> +static int tmp117_read_raw(struct iio_dev *indio_dev,
>> +        struct iio_chan_spec const *channel, int *val,
>> +        int *val2, long mask)
>> +{
>> +    struct tmp117_data *data = iio_priv(indio_dev);
>> +    u16 tmp, off;
>> +
>> +    switch (mask) {
>> +    case IIO_CHAN_INFO_RAW:
>> +        tmp = tmp117_read_reg(data, TMP117_REG_TEMP);
>> +        *val = tmp;
> No need for tmp here. Just directly assign to val.

Actually thinking about this, does the current implementation work 
correctly for negative temperatures?

I think there are two options to fix it. Either cast to s16 or use the 
sign_extend32() function.

Have a look at how the tmp006 driver handles this. It is a good example, 
including the error checking. In general you should check if your I2C 
read failed and return an error in that case rather than a bogus value 
for the measurement. Same for when reading the calibration offset.

Another thing. IIO reports temperature values in milli degrees Celsius. 
I believe in the current implementation the scale is so that it will 
report in degrees Celsius instead.