iio: adc: ad7124: Implement temperature measurement

If the maximal count of channels the driver supports isn't fully
utilized, add an attribute providing the internal temperature.

Signed-off-by: Uwe Kleine-König <[email protected]>
Link: https://patch.msgid.link/433211af8ac3f02dee58586ecb51d2e98246a095.1733504533.git.u.kleine-koenig@baylibre.com
Signed-off-by: Jonathan Cameron <[email protected]>
Origin: next-20241216~37^2~16, commit:6eaf3f60ab45a5740ed4e1a7d41c4f0c10f6ac3c

drivers/iio/adc/ad7124.c

@@ -94,6 +94,10 @@
 #define AD7124_MAX_CONFIGS	8
 #define AD7124_MAX_CHANNELS	16
 
+/* AD7124 input sources */
+#define AD7124_INPUT_TEMPSENSOR	16
+#define AD7124_INPUT_AVSS	17
+
 enum ad7124_ids {
 	ID_AD7124_4,
 	ID_AD7124_8,
@@ -596,26 +600,59 @@ static int ad7124_read_raw(struct iio_dev *indio_dev,
 
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
-		mutex_lock(&st->cfgs_lock);
+		switch (chan->type) {
+		case IIO_VOLTAGE:
+			mutex_lock(&st->cfgs_lock);
 
-		idx = st->channels[chan->address].cfg.pga_bits;
-		*val = st->channels[chan->address].cfg.vref_mv;
-		if (st->channels[chan->address].cfg.bipolar)
-			*val2 = chan->scan_type.realbits - 1 + idx;
-		else
-			*val2 = chan->scan_type.realbits + idx;
+			idx = st->channels[chan->address].cfg.pga_bits;
+			*val = st->channels[chan->address].cfg.vref_mv;
+			if (st->channels[chan->address].cfg.bipolar)
+				*val2 = chan->scan_type.realbits - 1 + idx;
+			else
+				*val2 = chan->scan_type.realbits + idx;
+
+			mutex_unlock(&st->cfgs_lock);
+			return IIO_VAL_FRACTIONAL_LOG2;
+
+		case IIO_TEMP:
+			/*
+			 * According to the data sheet
+			 *   Temperature (°C)
+			 * = ((Conversion − 0x800000)/13584) − 272.5
+			 * = (Conversion − 0x800000 - 13584 * 272.5) / 13584
+			 * = (Conversion − 12090248) / 13584
+			 * So scale with 1000/13584 to yield °mC. Reduce by 8 to
+			 * 125/1698.
+			 */
+			*val = 125;
+			*val2 = 1698;
+			return IIO_VAL_FRACTIONAL;
+
+		default:
+			return -EINVAL;
+		}
 
-		mutex_unlock(&st->cfgs_lock);
-		return IIO_VAL_FRACTIONAL_LOG2;
 	case IIO_CHAN_INFO_OFFSET:
-		mutex_lock(&st->cfgs_lock);
-		if (st->channels[chan->address].cfg.bipolar)
-			*val = -(1 << (chan->scan_type.realbits - 1));
-		else
-			*val = 0;
+		switch (chan->type) {
+		case IIO_VOLTAGE:
+			mutex_lock(&st->cfgs_lock);
+			if (st->channels[chan->address].cfg.bipolar)
+				*val = -(1 << (chan->scan_type.realbits - 1));
+			else
+				*val = 0;
+
+			mutex_unlock(&st->cfgs_lock);
+			return IIO_VAL_INT;
+
+		case IIO_TEMP:
+			/* see calculation above */
+			*val = -12090248;
+			return IIO_VAL_INT;
+
+		default:
+			return -EINVAL;
+		}
 
-		mutex_unlock(&st->cfgs_lock);
-		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		mutex_lock(&st->cfgs_lock);
 		*val = st->channels[chan->address].cfg.odr;
@@ -837,13 +874,10 @@ static int ad7124_of_parse_channel_config(struct iio_dev *indio_dev,
 	struct device_node *child;
 	struct iio_chan_spec *chan;
 	unsigned int ain[2], channel = 0, tmp;
+	unsigned int num_channels;
 	int ret;
 
-	st->num_channels = of_get_available_child_count(np);
-	if (!st->num_channels) {
-		dev_err(indio_dev->dev.parent, "no channel children\n");
-		return -ENODEV;
-	}
+	num_channels = of_get_available_child_count(np);
 
 	/*
 	 * The driver assigns each logical channel defined in the device tree
@@ -852,9 +886,12 @@ static int ad7124_of_parse_channel_config(struct iio_dev *indio_dev,
 	 * CHANNEL_15) as an additional channel register. The driver could be
 	 * improved to lift this limitation.
 	 */
-	if (st->num_channels > AD7124_MAX_CHANNELS)
+	if (num_channels > AD7124_MAX_CHANNELS)
 		return dev_err_probe(indio_dev->dev.parent, -EINVAL, "Too many channels defined\n");
 
+	/* Add one for temperature */
+	st->num_channels = min(num_channels + 1, (unsigned int)AD7124_MAX_CHANNELS);
+
 	chan = devm_kcalloc(indio_dev->dev.parent, st->num_channels,
 			    sizeof(*chan), GFP_KERNEL);
 	if (!chan)
@@ -874,7 +911,7 @@ static int ad7124_of_parse_channel_config(struct iio_dev *indio_dev,
 		if (ret)
 			goto err;
 
-		if (channel >= indio_dev->num_channels) {
+		if (channel >= num_channels) {
 			dev_err(indio_dev->dev.parent,
 				"Channel index >= number of channels\n");
 			ret = -EINVAL;
@@ -914,6 +951,37 @@ static int ad7124_of_parse_channel_config(struct iio_dev *indio_dev,
 		chan[channel].channel2 = ain[1];
 	}
 
+	if (num_channels < AD7124_MAX_CHANNELS) {
+		st->channels[num_channels] = (struct ad7124_channel) {
+			.nr = num_channels,
+			.ain = AD7124_CHANNEL_AINP(AD7124_INPUT_TEMPSENSOR) |
+				AD7124_CHANNEL_AINM(AD7124_INPUT_AVSS),
+			.cfg = {
+				.bipolar = true,
+			},
+		};
+
+		chan[num_channels] = (struct iio_chan_spec) {
+			.type = IIO_TEMP,
+			.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
+				BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET) |
+				BIT(IIO_CHAN_INFO_SAMP_FREQ),
+			.scan_type = {
+				/*
+				 * You might find it strange that a bipolar
+				 * measurement yields an unsigned value, but
+				 * this matches the device's manual.
+				 */
+				.sign = 'u',
+				.realbits = 24,
+				.storagebits = 32,
+				.endianness = IIO_BE,
+			},
+			.address = num_channels,
+			.scan_index = num_channels,
+		};
+	}
+
 	return 0;
 err:
 	of_node_put(child);