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authorBjorn Andersson <bjorn.andersson@linaro.org>2018-12-24 10:26:44 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-02-12 21:46:09 +0300
commit919fc06bf18b4e26d8d68f249f968b36c2e45dea (patch)
tree5a6d698cab2c7c6b9d1caa945f5896e3d5b5b925 /drivers
parenta67a554d53d627cd12232c15ef2b159808410ccb (diff)
downloadlinux-919fc06bf18b4e26d8d68f249f968b36c2e45dea.tar.xz
thermal: generic-adc: Fix adc to temp interpolation
[ Upstream commit 9d216211fded20fff301d0317af3238d8383634c ] 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> Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/thermal/thermal-generic-adc.c12
1 files changed, 8 insertions, 4 deletions
diff --git a/drivers/thermal/thermal-generic-adc.c b/drivers/thermal/thermal-generic-adc.c
index 73f55d6a1721..ad601e5b4175 100644
--- a/drivers/thermal/thermal-generic-adc.c
+++ b/drivers/thermal/thermal-generic-adc.c
@@ -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;