Re: [PATCH] thermal: generic-adc: Fix linear temperature approximation

[Laxman Dewangan <ldewangan@nvidia.com>]

On Thursday 20 October 2016 10:40 PM, Paweł Jarosz wrote:
>
>> Yes please send patch to replace the 1000 with the temp1 - temp2 as 
>> what you did in your original patch.
>> This will fix the non-sequenced (un-equally spaced) temperature table.
>
> replacing 1000 with (temp1 - temp2) is not enough as for example for 
> val = 9 and table
>
> <7000 8
>  9000 10>


It is Negative Coefficient Thermistor (NCT) and so adc reads are different.
Lower temp gives higher value.

So table should be

<7000 10
9000 8>;

temp1 = gti->lookup_table[2 * i];
temp2 = gti->lookup_table[2 * i - 2];

and then use in following equation.

>
>     adc_hi = gti->lookup_table[2 * i - 1];
>     adc_lo = gti->lookup_table[2 * i + 1];
>     temp = gti->lookup_table[2 * i];
>     temp -= (val - adc_lo) * (temp1 - temp2) / (adc_hi - adc_lo);
>
>

> adc_hi = 8
> adc_lo = 10
> temp = 9000 - (9 - 10) * (7000 - 9000) / (8 - 10)
> temp = 9000 - (-1) * (-2000) / (-2)
> temp = 9000 - (-1000) = 10000
>
> and for val = 9 temp should be 8000.
>
>

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