iio: adc: stm32-adc: add support of generic channels binding

Add support of generic IIO channel binding:
./devicetree/bindings/iio/adc/adc.yaml
Keep support of st,adc-channels and st,adc-diff-channels
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/20211014131228.4692-5-olivier.moysan@foss.st.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/stm32-adc.c

@@ -35,7 +35,7 @@
 #define STM32H7_BOOST_CLKRATE		20000000UL
 
 #define STM32_ADC_CH_MAX		20	/* max number of channels */
-#define STM32_ADC_CH_SZ			10	/* max channel name size */
+#define STM32_ADC_CH_SZ			16	/* max channel name size */
 #define STM32_ADC_MAX_SQ		16	/* SQ1..SQ16 */
 #define STM32_ADC_MAX_SMP		7	/* SMPx range is [0..7] */
 #define STM32_ADC_TIMEOUT_US		100000
@@ -1792,6 +1792,73 @@ static int stm32_adc_legacy_chan_init(struct iio_dev *indio_dev,
 	return scan_index;
 }
 
+static int stm32_adc_generic_chan_init(struct iio_dev *indio_dev,
+				       struct stm32_adc *adc,
+				       struct iio_chan_spec *channels)
+{
+	struct device_node *node = indio_dev->dev.of_node;
+	const struct stm32_adc_info *adc_info = adc->cfg->adc_info;
+	struct device_node *child;
+	const char *name;
+	int val, scan_index = 0, ret;
+	bool differential;
+	u32 vin[2];
+
+	for_each_available_child_of_node(node, child) {
+		ret = of_property_read_u32(child, "reg", &val);
+		if (ret) {
+			dev_err(&indio_dev->dev, "Missing channel index %d\n", ret);
+			goto err;
+		}
+
+		ret = of_property_read_string(child, "label", &name);
+		/* label is optional */
+		if (!ret) {
+			if (strlen(name) >= STM32_ADC_CH_SZ) {
+				dev_err(&indio_dev->dev, "Label %s exceeds %d characters\n",
+					name, STM32_ADC_CH_SZ);
+				return -EINVAL;
+			}
+			strncpy(adc->chan_name[val], name, STM32_ADC_CH_SZ);
+		} else if (ret != -EINVAL) {
+			dev_err(&indio_dev->dev, "Invalid label %d\n", ret);
+			goto err;
+		}
+
+		if (val >= adc_info->max_channels) {
+			dev_err(&indio_dev->dev, "Invalid channel %d\n", val);
+			ret = -EINVAL;
+			goto err;
+		}
+
+		differential = false;
+		ret = of_property_read_u32_array(child, "diff-channels", vin, 2);
+		/* diff-channels is optional */
+		if (!ret) {
+			differential = true;
+			if (vin[0] != val || vin[1] >= adc_info->max_channels) {
+				dev_err(&indio_dev->dev, "Invalid channel in%d-in%d\n",
+					vin[0], vin[1]);
+				goto err;
+			}
+		} else if (ret != -EINVAL) {
+			dev_err(&indio_dev->dev, "Invalid diff-channels property %d\n", ret);
+			goto err;
+		}
+
+		stm32_adc_chan_init_one(indio_dev, &channels[scan_index], val,
+					vin[1], scan_index, differential);
+		scan_index++;
+	}
+
+	return scan_index;
+
+err:
+	of_node_put(child);
+
+	return ret;
+}
+
 static int stm32_adc_chan_of_init(struct iio_dev *indio_dev, bool timestamping)
 {
 	struct device_node *node = indio_dev->dev.of_node;
@@ -1800,15 +1867,22 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev, bool timestamping)
 	struct iio_chan_spec *channels;
 	int scan_index = 0, num_channels = 0, ret, i;
 	u32 smp = 0;
+	bool legacy = false;
 
-	ret = stm32_adc_get_legacy_chan_count(indio_dev, adc);
-	if (ret < 0)
-		return ret;
-	num_channels = ret;
-
+	num_channels = of_get_available_child_count(node);
+	/* If no channels have been found, fallback to channels legacy properties. */
 	if (!num_channels) {
-		dev_err(&indio_dev->dev, "No channels configured\n");
-		return -ENODATA;
+		legacy = true;
+
+		ret = stm32_adc_get_legacy_chan_count(indio_dev, adc);
+		if (!ret) {
+			dev_err(indio_dev->dev.parent, "No channel found\n");
+			return -ENODATA;
+		} else if (ret < 0) {
+			return ret;
+		}
+
+		num_channels = ret;
 	}
 
 	if (num_channels > adc_info->max_channels) {
@@ -1832,7 +1906,10 @@ static int stm32_adc_chan_of_init(struct iio_dev *indio_dev, bool timestamping)
 	if (!channels)
 		return -ENOMEM;
 
-	ret = stm32_adc_legacy_chan_init(indio_dev, adc, channels);
+	if (legacy)
+		ret = stm32_adc_legacy_chan_init(indio_dev, adc, channels);
+	else
+		ret = stm32_adc_generic_chan_init(indio_dev, adc, channels);
 	if (ret < 0)
 		return ret;
 	scan_index = ret;