Re: [PATCH v2 2/9] thermal: qcom: tsens-8916: Add support for 8916 family of SoCs

[Rajendra Nayak <rnayak@codeaurora.org>]

On 09/21/2015 09:58 AM, Rajendra Nayak wrote:
> []..
> 
>>> +static inline int code_to_degc(u32 adc_code, const struct tsens_sensor *s)
>>> +{
>>> +    int degc, num, den;
>>> +
>>> +    num = (adc_code * SLOPE_FACTOR) - s->offset;
>>> +    den = s->slope;
>>> +
>>> +    if (num > 0)
>>> +        degc = num + (den / 2);
>>> +    else if (num < 0)
>>> +        degc = num - (den / 2);
>>> +    else
>>> +        degc = num;
>>> +
>>> +    degc /= den;
>>> +
>>> +    return degc;
>>> +}
>>> +
>>> +int get_temp_common(struct tsens_device *tmdev, int id, int *temp)
>>> +{
>>> +    struct tsens_sensor *s = &tmdev->sensor[id];
>>> +    u32 code;
>>> +    unsigned int sensor_addr;
>>> +    int last_temp = 0, ret;
>>> +
>>> +    sensor_addr = S0_ST_ADDR + s->hw_id * SN_ADDR_OFFSET;
>>> +    ret = regmap_read(tmdev->map, sensor_addr, &code);
>>> +    if (ret)
>>> +        return ret;
>>> +    last_temp = code & SN_ST_TEMP_MASK;
>>> +
>>> +    *temp = code_to_degc(last_temp, s) * 1000;
>>> +
>>> +    return 0;
>>> +}
>>
>> The way this function is coded the temperature will only ever change by
>> 1C (i.e., 1000mC). Is there a chance that you're losing precision in the
>> code_to_degc conversion that could be preserved perhaps?
>>
>> This is useful in scenarios where you use the power allocator governor
>> and the greater precision allows better power budget estimation.
> 
> I'll take a look to see if we can get better precision. Thanks.

I checked, and it does not look like these devices can support better precision
than degC.

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