iio: adc: stm32-adc: use generic binding for sample-time

Add st,min-sample-time-nsecs to channel generic binding.
Sample time can be defined par channel node. If a channel
is configured as differential, the same sample time applies
for both inputs.
Keep support of legacy st,min-sample-time-nsecs property
for backward compatibility.
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/20211014131228.4692-8-olivier.moysan@foss.st.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/stm32-adc.c

@@ -1805,6 +1805,13 @@ static void stm32_adc_smpr_init(struct stm32_adc *adc, int channel, u32 smp_ns)
 	u32 period_ns, shift = smpr->shift, mask = smpr->mask;
 	unsigned int smp, r = smpr->reg;
 
+	/*
+	 * For vrefint channel, ensure that the sampling time cannot
+	 * be lower than the one specified in the datasheet
+	 */
+	if (channel == adc->int_ch[STM32_ADC_INT_CH_VREFINT])
+		smp_ns = max(smp_ns, adc->cfg->ts_vrefint_ns);
+
 	/* Determine sampling time (ADC clock cycles) */
 	period_ns = NSEC_PER_SEC / adc->common->rate;
 	for (smp = 0; smp <= STM32_ADC_MAX_SMP; smp++)
@@ -1881,6 +1888,13 @@ static int stm32_adc_get_legacy_chan_count(struct iio_dev *indio_dev, struct stm
 		num_channels += ret;
 	}
 
+	/* Optional sample time is provided either for each, or all channels */
+	ret = of_property_count_u32_elems(node, "st,min-sample-time-nsecs");
+	if (ret > 1 && ret != num_channels) {
+		dev_err(&indio_dev->dev, "Invalid st,min-sample-time-nsecs\n");
+		return -EINVAL;
+	}
+
 	return num_channels;
 }
 
@@ -1896,6 +1910,7 @@ static int stm32_adc_legacy_chan_init(struct iio_dev *indio_dev,
 	int scan_index = 0, val, ret, i;
 	struct property *prop;
 	const __be32 *cur;
+	u32 smp = 0;
 
 	if (num_diff) {
 		ret = of_property_read_u32_array(node, "st,adc-diff-channels",
@@ -1938,6 +1953,19 @@ static int stm32_adc_legacy_chan_init(struct iio_dev *indio_dev,
 		scan_index++;
 	}
 
+	for (i = 0; i < scan_index; i++) {
+		/*
+		 * Using of_property_read_u32_index(), smp value will only be
+		 * modified if valid u32 value can be decoded. This allows to
+		 * get either no value, 1 shared value for all indexes, or one
+		 * value per channel.
+		 */
+		of_property_read_u32_index(node, "st,min-sample-time-nsecs", i, &smp);
+
+		/* Prepare sampling time settings */
+		stm32_adc_smpr_init(adc, channels[i].channel, smp);
+	}
+
 	return scan_index;
 }
 
@@ -2030,6 +2058,19 @@ static int stm32_adc_generic_chan_init(struct iio_dev *indio_dev,
 
 		stm32_adc_chan_init_one(indio_dev, &channels[scan_index], val,
 					vin[1], scan_index, differential);
+
+		ret = of_property_read_u32(child, "st,min-sample-time-ns", &val);
+		/* st,min-sample-time-ns is optional */
+		if (!ret) {
+			stm32_adc_smpr_init(adc, channels[scan_index].channel, val);
+			if (differential)
+				stm32_adc_smpr_init(adc, vin[1], val);
+		} else if (ret != -EINVAL) {
+			dev_err(&indio_dev->dev, "Invalid st,min-sample-time-ns property %d\n",
+				ret);
+			goto err;
+		}
+
 		scan_index++;
 	}
 
@@ -2048,7 +2089,6 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev, bool timestamping)
 	const struct stm32_adc_info *adc_info = adc->cfg->adc_info;
 	struct iio_chan_spec *channels;
 	int scan_index = 0, num_channels = 0, ret, i;
-	u32 smp = 0;
 	bool legacy = false;
 
 	for (i = 0; i < STM32_ADC_INT_CH_NB; i++)
@@ -2076,13 +2116,6 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev, bool timestamping)
 		return -EINVAL;
 	}
 
-	/* Optional sample time is provided either for each, or all channels */
-	ret = of_property_count_u32_elems(node, "st,min-sample-time-nsecs");
-	if (ret > 1 && ret != num_channels) {
-		dev_err(&indio_dev->dev, "Invalid st,min-sample-time-nsecs\n");
-		return -EINVAL;
-	}
-
 	if (timestamping)
 		num_channels++;
 
@@ -2099,27 +2132,6 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev, bool timestamping)
 		return ret;
 	scan_index = ret;
 
-	for (i = 0; i < scan_index; i++) {
-		/*
-		 * Using of_property_read_u32_index(), smp value will only be
-		 * modified if valid u32 value can be decoded. This allows to
-		 * get either no value, 1 shared value for all indexes, or one
-		 * value per channel.
-		 */
-		of_property_read_u32_index(node, "st,min-sample-time-nsecs",
-					   i, &smp);
-
-		/*
-		 * For vrefint channel, ensure that the sampling time cannot
-		 * be lower than the one specified in the datasheet
-		 */
-		if (channels[i].channel == adc->int_ch[STM32_ADC_INT_CH_VREFINT])
-			smp = max(smp, adc->cfg->ts_vrefint_ns);
-
-		/* Prepare sampling time settings */
-		stm32_adc_smpr_init(adc, channels[i].channel, smp);
-	}
-
 	if (timestamping) {
 		struct iio_chan_spec *timestamp = &channels[scan_index];