[PATCH] iio: adc: spmi-vadc: Fix overflow in output value normalization

[Ivan T. Ivanov]

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.iva...@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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