iio: adc: qcom-pm8xxx-xoadc: add support for reading channel labels

Implement the .read_label callback to allow userspace to identify ADC
channels via the "label" property in the device tree. The name field in
pm8xxx_chan_info is renamed to label to better reflect its purpose. If
no label is provided in the device tree, it defaults to the hardware
datasheet name.

The change has been tested on Sony Xperia SP (PM8921).

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Signed-off-by: Antony Kurniawan Soemardi <linux@smankusors.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Author: Smankusors

drivers/iio/adc/qcom-pm8xxx-xoadc.c

@@ -369,15 +369,15 @@ static const struct xoadc_channel pm8921_xoadc_channels[] = {
 
 /**
  * struct pm8xxx_chan_info - ADC channel information
- * @name: name of this channel
+ * @label: label of this channel from device tree (defaults to datasheet name if not specified)
  * @hwchan: pointer to hardware channel information (muxing & scaling settings)
  * @calibration: whether to use absolute or ratiometric calibration
  * @decimation: 0,1,2,3
  * @amux_ip_rsv: ratiometric scale value if using ratiometric
  * calibration: 0, 1, 2, 4, 5.
  */
 struct pm8xxx_chan_info {
-	const char *name;
+	const char *label;
 	const struct xoadc_channel *hwchan;
 	enum vadc_calibration calibration;
 	u8 decimation:2;
@@ -446,7 +446,7 @@ static int pm8xxx_read_channel_rsv(struct pm8xxx_xoadc *adc,
 	u8 lsb, msb;
 
 	dev_dbg(adc->dev, "read channel \"%s\", amux %d, prescale/mux: %d, rsv %d\n",
-		ch->name, ch->hwchan->amux_channel, ch->hwchan->pre_scale_mux, rsv);
+		ch->label, ch->hwchan->amux_channel, ch->hwchan->pre_scale_mux, rsv);
 
 	mutex_lock(&adc->lock);
 
@@ -716,8 +716,21 @@ static int pm8xxx_fwnode_xlate(struct iio_dev *indio_dev,
 	return -EINVAL;
 }
 
+static int pm8xxx_read_label(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan, char *label)
+{
+	struct pm8xxx_xoadc *adc = iio_priv(indio_dev);
+	const struct pm8xxx_chan_info *ch;
+
+	ch = pm8xxx_get_channel(adc, chan->address);
+	if (!ch)
+		return -EINVAL;
+	return sysfs_emit(label, "%s\n", ch->label);
+}
+
 static const struct iio_info pm8xxx_xoadc_info = {
 	.fwnode_xlate = pm8xxx_fwnode_xlate,
+	.read_label = pm8xxx_read_label,
 	.read_raw = pm8xxx_read_raw,
 };
 
@@ -761,7 +774,8 @@ static int pm8xxx_xoadc_parse_channel(struct device *dev,
 			pre_scale_mux, amux_channel);
 		return -EINVAL;
 	}
-	ch->name = name;
+	ch->label = hwchan->datasheet_name;
+	fwnode_property_read_string(fwnode, "label", &ch->label);
 	ch->hwchan = hwchan;
 	/* Everyone seems to use absolute calibration except in special cases */
 	ch->calibration = VADC_CALIB_ABSOLUTE;
@@ -803,7 +817,7 @@ static int pm8xxx_xoadc_parse_channel(struct device *dev,
 
 	dev_dbg(dev,
 		"channel [PRESCALE/MUX: %02x AMUX: %02x] \"%s\" ref voltage: %d, decimation %d prescale %d/%d, scale function %d\n",
-		hwchan->pre_scale_mux, hwchan->amux_channel, ch->name,
+		hwchan->pre_scale_mux, hwchan->amux_channel, ch->label,
 		ch->amux_ip_rsv, ch->decimation, hwchan->prescale.numerator,
 		hwchan->prescale.denominator, hwchan->scale_fn_type);