iio: imu: fxos8700: fix IMU data bits returned to user space

ACCEL output data registers contain the X-axis, Y-axis, and Z-axis
14-bit left-justified sample data and MAGN output data registers
contain the X-axis, Y-axis, and Z-axis 16-bit sample data. The ACCEL
raw register output data should be divided by 4 before sent to
userspace.

Apply a 2 bits signed right shift to the raw data from ACCEL output
data register but keep that from MAGN sensor as the origin.

Fixes: 84e5ddd5 ("iio: imu: Add support for the FXOS8700 IMU")
Signed-off-by: Carlos Song <carlos.song@nxp.com>
Link: https://lore.kernel.org/r/20221208071911.2405922-5-carlos.song@nxp.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/imu/fxos8700_core.c

@@ -394,6 +394,7 @@ static int fxos8700_get_data(struct fxos8700_data *data, int chan_type,
 			     int axis, int *val)
 {
 	u8 base, reg;
+	s16 tmp;
 	int ret;
 
 	/*
@@ -421,8 +422,33 @@ static int fxos8700_get_data(struct fxos8700_data *data, int chan_type,
 	/* Convert axis to buffer index */
 	reg = axis - IIO_MOD_X;
 
+	/*
+	 * Convert to native endianness. The accel data and magn data
+	 * are signed, so a forced type conversion is needed.
+	 */
+	tmp = be16_to_cpu(data->buf[reg]);
+
+	/*
+	 * ACCEL output data registers contain the X-axis, Y-axis, and Z-axis
+	 * 14-bit left-justified sample data and MAGN output data registers
+	 * contain the X-axis, Y-axis, and Z-axis 16-bit sample data. Apply
+	 * a signed 2 bits right shift to the readback raw data from ACCEL
+	 * output data register and keep that from MAGN sensor as the origin.
+	 * Value should be extended to 32 bit.
+	 */
+	switch (chan_type) {
+	case IIO_ACCEL:
+		tmp = tmp >> 2;
+		break;
+	case IIO_MAGN:
+		/* Nothing to do */
+		break;
+	default:
+		return -EINVAL;
+	}
+
 	/* Convert to native endianness */
-	*val = sign_extend32(be16_to_cpu(data->buf[reg]), 15);
+	*val = sign_extend32(tmp, 15);
 
 	return 0;
 }