iio: proximity: stk3310: Export near level property for proximity sensor

This makes the value from which an object should be considered "near"
available to userspace. This hardware-dependent value should be set
in the device-tree.
Signed-off-by: Arnaud Ferraris <arnaud.ferraris@collabora.com>
Link: https://lore.kernel.org/r/20220420112540.91907-3-arnaud.ferraris@collabora.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/light/stk3310.c

@@ -106,6 +106,7 @@ struct stk3310_data {
 	struct mutex lock;
 	bool als_enabled;
 	bool ps_enabled;
+	uint32_t ps_near_level;
 	u64 timestamp;
 	struct regmap *regmap;
 	struct regmap_field *reg_state;
@@ -135,6 +136,25 @@ static const struct iio_event_spec stk3310_events[] = {
 	},
 };
 
+static ssize_t stk3310_read_near_level(struct iio_dev *indio_dev,
+				       uintptr_t priv,
+				       const struct iio_chan_spec *chan,
+				       char *buf)
+{
+	struct stk3310_data *data = iio_priv(indio_dev);
+
+	return sprintf(buf, "%u\n", data->ps_near_level);
+}
+
+static const struct iio_chan_spec_ext_info stk3310_ext_info[] = {
+	{
+		.name = "nearlevel",
+		.shared = IIO_SEPARATE,
+		.read = stk3310_read_near_level,
+	},
+	{ /* sentinel */ }
+};
+
 static const struct iio_chan_spec stk3310_channels[] = {
 	{
 		.type = IIO_LIGHT,
@@ -151,6 +171,7 @@ static const struct iio_chan_spec stk3310_channels[] = {
 			BIT(IIO_CHAN_INFO_INT_TIME),
 		.event_spec = stk3310_events,
 		.num_event_specs = ARRAY_SIZE(stk3310_events),
+		.ext_info = stk3310_ext_info,
 	}
 };
 
@@ -581,6 +602,10 @@ static int stk3310_probe(struct i2c_client *client,
 	data = iio_priv(indio_dev);
 	data->client = client;
 	i2c_set_clientdata(client, indio_dev);
+
+	device_property_read_u32(&client->dev, "proximity-near-level",
+				 &data->ps_near_level);
+
 	mutex_init(&data->lock);
 
 	ret = stk3310_regmap_init(data);