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Subject[PATCH] iio: adc: spmi-vadc: Fix overflow in output value normalization
Date
With 'dx' equal to 0.625V and 15 bit ADC, calculations overflow
when difference against GND is ~20% of the ADC range. Fix this.

Signed-off-by: Ivan T. Ivanov <ivan.ivanov@linaro.org>
---
drivers/iio/adc/qcom-spmi-vadc.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/qcom-spmi-vadc.c b/drivers/iio/adc/qcom-spmi-vadc.c
index 3211729..0c4618b 100644
--- a/drivers/iio/adc/qcom-spmi-vadc.c
+++ b/drivers/iio/adc/qcom-spmi-vadc.c
@@ -18,6 +18,7 @@
#include <linux/iio/iio.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
+#include <linux/math64.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
@@ -471,11 +472,11 @@ static s32 vadc_calibrate(struct vadc_priv *vadc,
const struct vadc_channel_prop *prop, u16 adc_code)
{
const struct vadc_prescale_ratio *prescale;
- s32 voltage;
+ s64 voltage;

voltage = adc_code - vadc->graph[prop->calibration].gnd;
voltage *= vadc->graph[prop->calibration].dx;
- voltage = voltage / vadc->graph[prop->calibration].dy;
+ voltage = div64_s64(voltage, vadc->graph[prop->calibration].dy);

if (prop->calibration == VADC_CALIB_ABSOLUTE)
voltage += vadc->graph[prop->calibration].dx;
@@ -487,7 +488,7 @@ static s32 vadc_calibrate(struct vadc_priv *vadc,

voltage = voltage * prescale->den;

- return voltage / prescale->num;
+ return div64_s64(voltage, prescale->num);
}

static int vadc_decimation_from_dt(u32 value)
--
1.9.1


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