iio: adc: stm32: fix vrefint wrong calibration value handling

If the vrefint calibration is zero, the vrefint channel output value
cannot be computed. Currently, in such case, the raw conversion value
is returned, which is not relevant.
Do not expose the vrefint channel when the output value cannot be
computed, instead.

Fixes: 0e346b2 ("iio: adc: stm32-adc: add vrefint calibration support")
Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Reviewed-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20220609095856.376961-1-olivier.moysan@foss.st.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: Olivier Moysan

drivers/iio/adc/stm32-adc.c

@@ -1365,7 +1365,7 @@ static int stm32_adc_read_raw(struct iio_dev *indio_dev,
 		else
 			ret = -EINVAL;
 
-		if (mask == IIO_CHAN_INFO_PROCESSED && adc->vrefint.vrefint_cal)
+		if (mask == IIO_CHAN_INFO_PROCESSED)
 			*val = STM32_ADC_VREFINT_VOLTAGE * adc->vrefint.vrefint_cal / *val;
 
 		iio_device_release_direct_mode(indio_dev);
@@ -1969,21 +1969,26 @@ static int stm32_adc_populate_int_ch(struct iio_dev *indio_dev, const char *ch_n
 
 	for (i = 0; i < STM32_ADC_INT_CH_NB; i++) {
 		if (!strncmp(stm32_adc_ic[i].name, ch_name, STM32_ADC_CH_SZ)) {
-			adc->int_ch[i] = chan;
-
-			if (stm32_adc_ic[i].idx != STM32_ADC_INT_CH_VREFINT)
-				continue;
+			if (stm32_adc_ic[i].idx != STM32_ADC_INT_CH_VREFINT) {
+				adc->int_ch[i] = chan;
+				break;
+			}
 
 			/* Get calibration data for vrefint channel */
 			ret = nvmem_cell_read_u16(&indio_dev->dev, "vrefint", &vrefint);
 			if (ret && ret != -ENOENT) {
 				return dev_err_probe(indio_dev->dev.parent, ret,
 						     "nvmem access error\n");
 			}
-			if (ret == -ENOENT)
-				dev_dbg(&indio_dev->dev, "vrefint calibration not found\n");
-			else
-				adc->vrefint.vrefint_cal = vrefint;
+			if (ret == -ENOENT) {
+				dev_dbg(&indio_dev->dev, "vrefint calibration not found. Skip vrefint channel\n");
+				return ret;
+			} else if (!vrefint) {
+				dev_dbg(&indio_dev->dev, "Null vrefint calibration value. Skip vrefint channel\n");
+				return -ENOENT;
+			}
+			adc->int_ch[i] = chan;
+			adc->vrefint.vrefint_cal = vrefint;
 		}
 	}
 
@@ -2020,7 +2025,9 @@ static int stm32_adc_generic_chan_init(struct iio_dev *indio_dev,
 			}
 			strncpy(adc->chan_name[val], name, STM32_ADC_CH_SZ);
 			ret = stm32_adc_populate_int_ch(indio_dev, name, val);
-			if (ret)
+			if (ret == -ENOENT)
+				continue;
+			else if (ret)
 				goto err;
 		} else if (ret != -EINVAL) {
 			dev_err(&indio_dev->dev, "Invalid label %d\n", ret);