iio: dps310: Temperature measurement errata

Add a manufacturer's suggested workaround to deal with early revisions
of chip that don't indicate correct temperature. Readings can be in the
~60C range when they should be in the ~20's.
Signed-off-by: Christopher Bostic <cbostic@linux.vnet.ibm.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/pressure/dps310.c

@@ -53,7 +53,6 @@
 #define DPS310_RESET		0x0c
 #define  DPS310_RESET_MAGIC	0x09
 #define DPS310_COEF_BASE	0x10
-#define DPS310_COEF_SRC		0x28
 
 /* Make sure sleep time is <= 20ms for usleep_range */
 #define DPS310_POLL_SLEEP_US(t)		min(20000, (t) / 8)
@@ -234,6 +233,10 @@ static bool dps310_is_writeable_reg(struct device *dev, unsigned int reg)
 	case DPS310_MEAS_CFG:
 	case DPS310_CFG_REG:
 	case DPS310_RESET:
+	/* No documentation available on the registers below */
+	case 0x0e:
+	case 0x0f:
+	case 0x62:
 		return true;
 	default:
 		return false;
@@ -250,6 +253,7 @@ static bool dps310_is_volatile_reg(struct device *dev, unsigned int reg)
 	case DPS310_TMP_B1:
 	case DPS310_TMP_B2:
 	case DPS310_MEAS_CFG:
+	case 0x32:	/* No documentation available on this register */
 		return true;
 	default:
 		return false;
@@ -360,7 +364,7 @@ static const struct regmap_config dps310_regmap_config = {
 	.writeable_reg = dps310_is_writeable_reg,
 	.volatile_reg = dps310_is_volatile_reg,
 	.cache_type = REGCACHE_RBTREE,
-	.max_register = DPS310_COEF_SRC,
+	.max_register = 0x62, /* No documentation available on this register */
 };
 
 static const struct iio_info dps310_info = {
@@ -368,6 +372,46 @@ static const struct iio_info dps310_info = {
 	.write_raw = dps310_write_raw,
 };
 
+/*
+ * Some verions of chip will read temperatures in the ~60C range when
+ * its actually ~20C. This is the manufacturer recommended workaround
+ * to correct the issue. The registers used below are undocumented.
+ */
+static int dps310_temp_workaround(struct dps310_data *data)
+{
+	int rc;
+	int reg;
+
+	rc = regmap_read(data->regmap, 0x32, &reg);
+	if (rc < 0)
+		return rc;
+
+	/*
+	 * If bit 1 is set then the device is okay, and the workaround does not
+	 * need to be applied
+	 */
+	if (reg & BIT(1))
+		return 0;
+
+	rc = regmap_write(data->regmap, 0x0e, 0xA5);
+	if (rc < 0)
+		return rc;
+
+	rc = regmap_write(data->regmap, 0x0f, 0x96);
+	if (rc < 0)
+		return rc;
+
+	rc = regmap_write(data->regmap, 0x62, 0x02);
+	if (rc < 0)
+		return rc;
+
+	rc = regmap_write(data->regmap, 0x0e, 0x00);
+	if (rc < 0)
+		return rc;
+
+	return regmap_write(data->regmap, 0x0f, 0x00);
+}
+
 static int dps310_probe(struct i2c_client *client,
 			const struct i2c_device_id *id)
 {
@@ -439,6 +483,10 @@ static int dps310_probe(struct i2c_client *client,
 	if (rc < 0)
 		return rc;
 
+	rc = dps310_temp_workaround(data);
+	if (rc < 0)
+		return rc;
+
 	rc = devm_iio_device_register(&client->dev, iio);
 	if (rc)
 		return rc;