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thermal: generic-adc: Fix adc to temp interpolation

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First correct the edge case to return the last element if we're
outside the range, rather than at the last element, so that
interpolation is not omitted for points between the two last entries in
the table.

Then correct the formula to perform linear interpolation based the two
points surrounding the read ADC value. The indices for temp are kept as
"hi" and "lo" to pair with the adc indices, but there's no requirement
that the temperature is provided in descendent order. mult_frac() is
used to prevent issues with overflowing the int.

Cc: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>
This commit is contained in:
Bjorn Andersson 2018-12-23 23:26:44 -08:00 committed by Eduardo Valentin
parent e36e13003e
commit 9d216211fd
1 changed files with 8 additions and 4 deletions
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12
drivers/thermal/thermal-generic-adc.c
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@ -26,7 +26,7 @@ struct gadc_thermal_info {
static int gadc_thermal_adc_to_temp(struct gadc_thermal_info *gti, int val)
{
int temp, adc_hi, adc_lo;
int temp, temp_hi, temp_lo, adc_hi, adc_lo;
int i;
for (i = 0; i < gti->nlookup_table; i++) {
@ -36,13 +36,17 @@ static int gadc_thermal_adc_to_temp(struct gadc_thermal_info *gti, int val)
if (i == 0) {
temp = gti->lookup_table[0];
} else if (i >= (gti->nlookup_table - 1)) {
} else if (i >= gti->nlookup_table) {
temp = gti->lookup_table[2 * (gti->nlookup_table - 1)];
} else {
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) * 1000) / (adc_hi - adc_lo);
temp_hi = gti->lookup_table[2 * i - 2];
temp_lo = gti->lookup_table[2 * i];
temp = temp_hi + mult_frac(temp_lo - temp_hi, val - adc_hi,
adc_lo - adc_hi);
}
return temp;