[PATCH v2] iio: chemical: scd4x: Add pressure compensation

[Roan van Dijk <roan@protonic.nl>]

This patch adds pressure compensation to the scd4x driver. The pressure can
be written to the sensor in hPa. The pressure will be compensated
internally by the sensor.

Signed-off-by: Roan van Dijk <roan@protonic.nl>
---

Changes since v2:
 - Fix for kernel test robot errors of uninitialized symbols
 - Changed pressure compensation to output channel instead of a channel
   with calibbias
 - Pressure can now be compensated during measurements

 drivers/iio/chemical/scd4x.c | 79 +++++++++++++++++++++++++++++++++---
 1 file changed, 73 insertions(+), 6 deletions(-)

diff --git a/drivers/iio/chemical/scd4x.c b/drivers/iio/chemical/scd4x.c
index a4f22d926400..4bb5d215c54c 100644
--- a/drivers/iio/chemical/scd4x.c
+++ b/drivers/iio/chemical/scd4x.c
@@ -36,6 +36,8 @@
 #define SCD4X_WRITE_BUF_SIZE 5
 #define SCD4X_FRC_MIN_PPM 0
 #define SCD4X_FRC_MAX_PPM 2000
+#define SCD4X_PRESSURE_COMP_MIN_MBAR 700
+#define SCD4X_PRESSURE_COMP_MAX_MBAR 1200
 #define SCD4X_READY_MASK 0x01
 
 /*Commands SCD4X*/
@@ -45,6 +47,8 @@ enum scd4x_cmd {
 	CMD_STOP_MEAS           = 0x3f86,
 	CMD_SET_TEMP_OFFSET     = 0x241d,
 	CMD_GET_TEMP_OFFSET     = 0x2318,
+	CMD_SET_AMB_PRESSURE	= 0xe000,
+	CMD_GET_AMB_PRESSURE	= 0xe000,
 	CMD_FRC                 = 0x362f,
 	CMD_SET_ASC             = 0x2416,
 	CMD_GET_ASC             = 0x2313,
@@ -137,7 +141,8 @@ static int scd4x_read(struct scd4x_state *state, enum scd4x_cmd cmd,
 	 * Measurement needs to be stopped before sending commands.
 	 * Except for reading measurement and data ready command.
 	 */
-	if ((cmd != CMD_GET_DATA_READY) && (cmd != CMD_READ_MEAS)) {
+	if ((cmd != CMD_GET_DATA_READY) && (cmd != CMD_READ_MEAS) &&
+			(cmd != CMD_GET_AMB_PRESSURE)) {
 		ret = scd4x_send_command(state, CMD_STOP_MEAS);
 		if (ret)
 			return ret;
@@ -166,7 +171,8 @@ static int scd4x_read(struct scd4x_state *state, enum scd4x_cmd cmd,
 	}
 
 	/* start measurement */
-	if ((cmd != CMD_GET_DATA_READY) && (cmd != CMD_READ_MEAS)) {
+	if ((cmd != CMD_GET_DATA_READY) && (cmd != CMD_READ_MEAS) &&
+			(cmd != CMD_GET_AMB_PRESSURE)) {
 		ret = scd4x_send_command(state, CMD_START_MEAS);
 		if (ret)
 			return ret;
@@ -188,9 +194,11 @@ static int scd4x_write(struct scd4x_state *state, enum scd4x_cmd cmd, uint16_t a
 	buf[4] = crc;
 
 	/* measurement needs to be stopped before sending commands */
-	ret = scd4x_send_command(state, CMD_STOP_MEAS);
-	if (ret)
-		return ret;
+	if (cmd != CMD_SET_AMB_PRESSURE) {
+		ret = scd4x_send_command(state, CMD_STOP_MEAS);
+		if (ret)
+			return ret;
+	}
 
 	/* execution time */
 	msleep_interruptible(500);
@@ -200,7 +208,7 @@ static int scd4x_write(struct scd4x_state *state, enum scd4x_cmd cmd, uint16_t a
 		return ret;
 
 	/* start measurement, except for forced calibration command */
-	if (cmd != CMD_FRC) {
+	if ((cmd != CMD_FRC) && (cmd != CMD_SET_AMB_PRESSURE)) {
 		ret = scd4x_send_command(state, CMD_START_MEAS);
 		if (ret)
 			return ret;
@@ -338,6 +346,18 @@ static int scd4x_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
+		if (chan->output) {
+			mutex_lock(&state->lock);
+			ret = scd4x_read(state, CMD_GET_AMB_PRESSURE, &tmp, sizeof(tmp));
+			mutex_unlock(&state->lock);
+
+			if (ret)
+				return ret;
+
+			*val = be16_to_cpu(tmp);
+			return IIO_VAL_INT;
+		}
+
 		ret = iio_device_claim_direct_mode(indio_dev);
 		if (ret)
 			return ret;
@@ -386,6 +406,25 @@ static int scd4x_read_raw(struct iio_dev *indio_dev,
 	}
 }
 
+static const int scd4x_pressure_calibbias_available[] = {
+	SCD4X_PRESSURE_COMP_MIN_MBAR, 1, SCD4X_PRESSURE_COMP_MAX_MBAR,
+};
+
+static int scd4x_read_avail(struct iio_dev *indio_dev, struct iio_chan_spec const *chan,
+			    const int **vals, int *type, int *length, long mask)
+{
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		*vals = scd4x_pressure_calibbias_available;
+		*type = IIO_VAL_INT;
+
+		return IIO_AVAIL_RANGE;
+	}
+
+	return -EINVAL;
+}
+
+
 static int scd4x_write_raw(struct iio_dev *indio_dev, struct iio_chan_spec const *chan,
 				int val, int val2, long mask)
 {
@@ -399,6 +438,21 @@ static int scd4x_write_raw(struct iio_dev *indio_dev, struct iio_chan_spec const
 		mutex_unlock(&state->lock);
 
 		return ret;
+	case IIO_CHAN_INFO_RAW:
+		switch (chan->type) {
+		case IIO_PRESSURE:
+			if (val < SCD4X_PRESSURE_COMP_MIN_MBAR ||
+			    val > SCD4X_PRESSURE_COMP_MAX_MBAR)
+				return -EINVAL;
+
+			mutex_lock(&state->lock);
+			ret = scd4x_write(state, CMD_SET_AMB_PRESSURE, val);
+			mutex_unlock(&state->lock);
+
+			return ret;
+		default:
+			return -EINVAL;
+		}
 	default:
 		return -EINVAL;
 	}
@@ -503,9 +557,22 @@ static const struct iio_info scd4x_info = {
 	.attrs = &scd4x_attr_group,
 	.read_raw = scd4x_read_raw,
 	.write_raw = scd4x_write_raw,
+	.read_avail = scd4x_read_avail,
 };
 
 static const struct iio_chan_spec scd4x_channels[] = {
+	{
+		/*
+		 * this channel is special in a sense we are pretending that
+		 * sensor is able to change measurement chamber pressure but in
+		 * fact we're just setting pressure compensation value
+		 */
+		.type = IIO_PRESSURE,
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
+		.info_mask_separate_available = BIT(IIO_CHAN_INFO_RAW),
+		.output = 1,
+		.scan_index = -1,
+	},
 	{
 		.type = IIO_CONCENTRATION,
 		.channel2 = IIO_MOD_CO2,
-- 
2.39.2