iio: humidity: si7020: add heater support

This patch adds support for the integrated on-chip heater that is present
on all the devices supported by this driver (si7020, si7021, si7013, th6).
In order to configure the heater, the driver interacts with the following
device registers:
* User Register - the 2nd bit of this register is a "Heater Enable bit"
  (0 means that the heater is off, 1 means that it's on).
* Heater Register - this register is present only on the si70xx devices
  and controls the current flowing through the heater. The 4 lower bits
  of this register can be assigned values from 0x0 to 0xF.
Signed-off-by: Antoni Pokusinski <apokusinski01@gmail.com>
Link: https://lore.kernel.org/r/20240607141029.51744-1-apokusinski@o2.plSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/humidity/si7020.c

@@ -23,6 +23,7 @@
 #include <linux/mod_devicetable.h>
 #include <linux/slab.h>
 #include <linux/sysfs.h>
+#include <linux/stat.h>
 
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
@@ -33,17 +34,38 @@
 #define SI7020CMD_TEMP_HOLD	0xE3
 /* Software Reset */
 #define SI7020CMD_RESET		0xFE
+#define SI7020CMD_USR_WRITE	0xE6
+/* "Heater Enabled" bit in the User Register */
+#define SI7020_USR_HEATER_EN	BIT(2)
+#define SI7020CMD_HEATER_WRITE	0x51
+/* Heater current configuration bits */
+#define SI7020_HEATER_VAL	GENMASK(3, 0)
+
+struct si7020_data {
+	struct i2c_client *client;
+	/* Lock for cached register values */
+	struct mutex lock;
+	u8 user_reg;
+	u8 heater_reg;
+};
+
+static const int si7020_heater_vals[] = { 0, 1, 0xF };
 
 static int si7020_read_raw(struct iio_dev *indio_dev,
 			   struct iio_chan_spec const *chan, int *val,
 			   int *val2, long mask)
 {
-	struct i2c_client **client = iio_priv(indio_dev);
+	struct si7020_data *data = iio_priv(indio_dev);
 	int ret;
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		ret = i2c_smbus_read_word_swapped(*client,
+		if (chan->type == IIO_CURRENT) {
+			*val = data->heater_reg;
+			return IIO_VAL_INT;
+		}
+
+		ret = i2c_smbus_read_word_swapped(data->client,
 						  chan->type == IIO_TEMP ?
 						  SI7020CMD_TEMP_HOLD :
 						  SI7020CMD_RH_HOLD);
@@ -96,17 +118,118 @@ static const struct iio_chan_spec si7020_channels[] = {
 		.type = IIO_TEMP,
 		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
 			BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),
+	},
+	{
+		.type = IIO_CURRENT,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.info_mask_separate_available = BIT(IIO_CHAN_INFO_RAW),
+		.extend_name = "heater",
+	}
+};
+
+static int si7020_update_reg(struct si7020_data *data,
+				u8 *reg, u8 cmd, u8 mask, u8 val)
+{
+	u8 new = (*reg & ~mask) | val;
+	int ret;
+
+	ret = i2c_smbus_write_byte_data(data->client, cmd, new);
+	if (ret)
+		return ret;
+
+	*reg = new;
+
+	return 0;
+}
+
+static int si7020_write_raw(struct iio_dev *indio_dev,
+			     struct iio_chan_spec const *chan,
+			     int val, int val2, long mask)
+{
+	struct si7020_data *data = iio_priv(indio_dev);
+	int ret;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		if (chan->type != IIO_CURRENT || val2 != 0 ||
+			val < si7020_heater_vals[0] || val > si7020_heater_vals[2])
+			return -EINVAL;
+
+		scoped_guard(mutex, &data->lock)
+			ret = si7020_update_reg(data, &data->heater_reg,
+					SI7020CMD_HEATER_WRITE, SI7020_HEATER_VAL, val);
+		return ret;
+	default:
+		return -EINVAL;
 	}
+}
+
+static int si7020_read_available(struct iio_dev *indio_dev,
+				  struct iio_chan_spec const *chan,
+				  const int **vals,
+				  int *type, int *length, long mask)
+{
+	if (mask != IIO_CHAN_INFO_RAW || chan->type != IIO_CURRENT)
+		return -EINVAL;
+
+	*vals = si7020_heater_vals;
+	*type = IIO_VAL_INT;
+
+	return IIO_AVAIL_RANGE;
+}
+
+static ssize_t si7020_show_heater_en(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct si7020_data *data = iio_priv(indio_dev);
+
+	return sysfs_emit(buf, "%d\n", !!(data->user_reg & SI7020_USR_HEATER_EN));
+}
+
+static ssize_t si7020_store_heater_en(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t len)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct si7020_data *data = iio_priv(indio_dev);
+	int ret;
+	bool val;
+
+	ret = kstrtobool(buf, &val);
+	if (ret)
+		return ret;
+
+	scoped_guard(mutex, &data->lock)
+		ret = si7020_update_reg(data, &data->user_reg, SI7020CMD_USR_WRITE,
+				SI7020_USR_HEATER_EN, val ? SI7020_USR_HEATER_EN : 0);
+
+	return ret < 0 ? ret : len;
+}
+
+static IIO_DEVICE_ATTR(heater_enable, 0644,
+		       si7020_show_heater_en, si7020_store_heater_en, 0);
+
+static struct attribute *si7020_attributes[] = {
+	&iio_dev_attr_heater_enable.dev_attr.attr,
+	NULL
+};
+
+static const struct attribute_group si7020_attribute_group = {
+	.attrs = si7020_attributes,
 };
 
 static const struct iio_info si7020_info = {
 	.read_raw = si7020_read_raw,
+	.write_raw = si7020_write_raw,
+	.read_avail = si7020_read_available,
+	.attrs = &si7020_attribute_group,
 };
 
 static int si7020_probe(struct i2c_client *client)
 {
 	struct iio_dev *indio_dev;
-	struct i2c_client **data;
+	struct si7020_data *data;
 	int ret;
 
 	if (!i2c_check_functionality(client->adapter,
@@ -126,7 +249,9 @@ static int si7020_probe(struct i2c_client *client)
 		return -ENOMEM;
 
 	data = iio_priv(indio_dev);
-	*data = client;
+	i2c_set_clientdata(client, indio_dev);
+	data->client = client;
+	mutex_init(&data->lock);
 
 	indio_dev->name = dev_name(&client->dev);
 	indio_dev->modes = INDIO_DIRECT_MODE;
@@ -134,6 +259,10 @@ static int si7020_probe(struct i2c_client *client)
 	indio_dev->channels = si7020_channels;
 	indio_dev->num_channels = ARRAY_SIZE(si7020_channels);
 
+	/* All the "reserved" bits in the User Register are 1s by default */
+	data->user_reg = 0x3A;
+	data->heater_reg = 0x0;
+
 	return devm_iio_device_register(&client->dev, indio_dev);
 }