iio: adc: ad7768-1: Add channel label example

This is a demo usage of new "label" attribute for channel.

Signed-off-by: Cristian Pop <cristian.pop@analog.com>

drivers/iio/adc/ad7768-1.c

@@ -161,6 +161,7 @@ struct ad7768_state {
 	struct completion completion;
 	struct iio_trigger *trig;
 	struct gpio_desc *gpio_sync_in;
+	const char **labels;
 	/*
 	 * DMA (thus cache coherency maintenance) requires the
 	 * transfer buffers to live in their own cache lines.
@@ -407,6 +408,14 @@ static int ad7768_write_raw(struct iio_dev *indio_dev,
 	}
 }
 
+static int ad7768_read_label(struct iio_dev *indio_dev,
+	const struct iio_chan_spec *chan, char *label)
+{
+	struct ad7768_state *st = iio_priv(indio_dev);
+
+	return sprintf(label, "%s\n", st->labels[chan->channel]);
+}
+
 static struct attribute *ad7768_attributes[] = {
 	&iio_dev_attr_sampling_frequency_available.dev_attr.attr,
 	NULL
@@ -420,6 +429,7 @@ static const struct iio_info ad7768_info = {
 	.attrs = &ad7768_group,
 	.read_raw = &ad7768_read_raw,
 	.write_raw = &ad7768_write_raw,
+	.read_label = ad7768_read_label,
 	.debugfs_reg_access = &ad7768_reg_access,
 };
 
@@ -532,6 +542,41 @@ static void ad7768_clk_disable(void *data)
 	clk_disable_unprepare(st->mclk);
 }
 
+static int ad7768_set_channel_label(struct iio_dev *indio_dev,
+						int num_channels)
+{
+	struct ad7768_state *st = iio_priv(indio_dev);
+	struct device *device = indio_dev->dev.parent;
+	struct fwnode_handle *fwnode;
+	struct fwnode_handle *child;
+	const char *label;
+	int crt_ch = 0;
+
+	st->labels = devm_kcalloc(indio_dev->dev.parent,
+					num_channels,
+					sizeof(**st->labels),
+					GFP_KERNEL);
+
+	if (!st->labels)
+		return -ENOMEM;
+
+	fwnode = dev_fwnode(device);
+	fwnode_for_each_child_node(fwnode, child) {
+		if (fwnode_property_read_u32(child, "reg", &crt_ch))
+			continue;
+
+		if (crt_ch >= num_channels)
+			continue;
+
+		if (fwnode_property_read_string(child, "label", &label))
+			continue;
+
+		st->labels[crt_ch] = label;
+	}
+
+	return 0;
+}
+
 static int ad7768_probe(struct spi_device *spi)
 {
 	struct ad7768_state *st;
@@ -604,6 +649,10 @@ static int ad7768_probe(struct spi_device *spi)
 
 	init_completion(&st->completion);
 
+	ret = ad7768_set_channel_label(indio_dev, ARRAY_SIZE(ad7768_channels));
+	if (ret)
+		return ret;
+
 	ret = devm_request_irq(&spi->dev, spi->irq,
 			       &ad7768_interrupt,
 			       IRQF_TRIGGER_RISING | IRQF_ONESHOT,