iio: magnetometer: ak8975: Fix reading for ak099xx sensors

Move ST2 reading with overflow handling after measurement data
reading.
ST2 register read have to be read after read measurment data,
because it means end of the reading and realease the lock on the data.
Remove ST2 read skip on interrupt based waiting because ST2 required to
be read out at and of the axis read.

Fixes: 57e73a4 ("iio: ak8975: add ak09911 and ak09912 support")
Signed-off-by: Barnabás Czémán <barnabas.czeman@mainlining.org>
Link: https://patch.msgid.link/20240819-ak09918-v4-2-f0734d14cfb9@mainlining.org
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: barni2000

drivers/iio/magnetometer/ak8975.c

@@ -696,22 +696,8 @@ static int ak8975_start_read_axis(struct ak8975_data *data,
 	if (ret < 0)
 		return ret;
 
-	/* This will be executed only for non-interrupt based waiting case */
-	if (ret & data->def->ctrl_masks[ST1_DRDY]) {
-		ret = i2c_smbus_read_byte_data(client,
-					       data->def->ctrl_regs[ST2]);
-		if (ret < 0) {
-			dev_err(&client->dev, "Error in reading ST2\n");
-			return ret;
-		}
-		if (ret & (data->def->ctrl_masks[ST2_DERR] |
-			   data->def->ctrl_masks[ST2_HOFL])) {
-			dev_err(&client->dev, "ST2 status error 0x%x\n", ret);
-			return -EINVAL;
-		}
-	}
-
-	return 0;
+	/* Return with zero if the data is ready. */
+	return !data->def->ctrl_regs[ST1_DRDY];
 }
 
 /* Retrieve raw flux value for one of the x, y, or z axis.  */
@@ -738,6 +724,20 @@ static int ak8975_read_axis(struct iio_dev *indio_dev, int index, int *val)
 	if (ret < 0)
 		goto exit;
 
+	/* Read out ST2 for release lock on measurment data. */
+	ret = i2c_smbus_read_byte_data(client, data->def->ctrl_regs[ST2]);
+	if (ret < 0) {
+		dev_err(&client->dev, "Error in reading ST2\n");
+		goto exit;
+	}
+
+	if (ret & (data->def->ctrl_masks[ST2_DERR] |
+		   data->def->ctrl_masks[ST2_HOFL])) {
+		dev_err(&client->dev, "ST2 status error 0x%x\n", ret);
+		ret = -EINVAL;
+		goto exit;
+	}
+
 	mutex_unlock(&data->lock);
 
 	pm_runtime_mark_last_busy(&data->client->dev);