[PATCH v3 2/2] iio: adc: stm32-adc: skip adc-channels setup if none is present

[Sean Nyekjaer <sean@geanix.com>]

If only adc differential channels are defined driver will fail with
stm32-adc: probe of 48003000.adc:adc@0 failed with error -22

Fix this by skipping the initialization if no channels are defined.

This applies only to the legacy way of initializing adc channels.

Fixes: d7705f35448a ("iio: adc: stm32-adc: convert to device properties")
Signed-off-by: Sean Nyekjaer <sean@geanix.com>
---
Changes since v1:
- Ignore extra channel for timestamps in PIO mode
- Use single ended count in channel creation (Thanks Olivier Moysan)

Changes since v2:
- Avoid calling device_property_read_u32_array with num_se 0 (Thanks Olivier Moysan)

 drivers/iio/adc/stm32-adc.c | 42 ++++++++++++++++++++-----------------
 1 file changed, 23 insertions(+), 19 deletions(-)

diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
index 14524c1b5583..f7613efb870d 100644
--- a/drivers/iio/adc/stm32-adc.c
+++ b/drivers/iio/adc/stm32-adc.c
@@ -2038,6 +2038,7 @@ static int stm32_adc_legacy_chan_init(struct iio_dev *indio_dev,
 	struct stm32_adc_diff_channel diff[STM32_ADC_CH_MAX];
 	struct device *dev = &indio_dev->dev;
 	u32 num_diff = adc->num_diff;
+	int num_se = nchans - num_diff;
 	int size = num_diff * sizeof(*diff) / sizeof(u32);
 	int scan_index = 0, ret, i, c;
 	u32 smp = 0, smps[STM32_ADC_CH_MAX], chans[STM32_ADC_CH_MAX];
@@ -2064,29 +2065,32 @@ static int stm32_adc_legacy_chan_init(struct iio_dev *indio_dev,
 			scan_index++;
 		}
 	}
-
-	ret = device_property_read_u32_array(dev, "st,adc-channels", chans,
-					     nchans);
-	if (ret)
-		return ret;
-
-	for (c = 0; c < nchans; c++) {
-		if (chans[c] >= adc_info->max_channels) {
-			dev_err(&indio_dev->dev, "Invalid channel %d\n",
-				chans[c]);
-			return -EINVAL;
+	if (num_se > 0) {
+		ret = device_property_read_u32_array(dev, "st,adc-channels", chans, num_se);
+		if (ret) {
+			dev_err(&indio_dev->dev, "Failed to get st,adc-channels %d\n", ret);
+			return ret;
 		}
 
-		/* Channel can't be configured both as single-ended & diff */
-		for (i = 0; i < num_diff; i++) {
-			if (chans[c] == diff[i].vinp) {
-				dev_err(&indio_dev->dev, "channel %d misconfigured\n",	chans[c]);
+		for (c = 0; c < num_se; c++) {
+			if (chans[c] >= adc_info->max_channels) {
+				dev_err(&indio_dev->dev, "Invalid channel %d\n",
+					chans[c]);
 				return -EINVAL;
 			}
+
+			/* Channel can't be configured both as single-ended & diff */
+			for (i = 0; i < num_diff; i++) {
+				if (chans[c] == diff[i].vinp) {
+					dev_err(&indio_dev->dev, "channel %d misconfigured\n",
+						chans[c]);
+					return -EINVAL;
+				}
+			}
+			stm32_adc_chan_init_one(indio_dev, &channels[scan_index],
+						chans[c], 0, scan_index, false);
+			scan_index++;
 		}
-		stm32_adc_chan_init_one(indio_dev, &channels[scan_index],
-					chans[c], 0, scan_index, false);
-		scan_index++;
 	}
 
 	if (adc->nsmps > 0) {
@@ -2307,7 +2311,7 @@ static int stm32_adc_chan_fw_init(struct iio_dev *indio_dev, bool timestamping)
 
 	if (legacy)
 		ret = stm32_adc_legacy_chan_init(indio_dev, adc, channels,
-						 num_channels);
+						 timestamping ? num_channels - 1 : num_channels);
 	else
 		ret = stm32_adc_generic_chan_init(indio_dev, adc, channels);
 	if (ret < 0)
-- 
2.40.0