[PATCH] iio: magnetometer: st_magn: fix default DRDY pin selection for LIS2MDL

[Advait Dhamorikar <advaitd@mechasystems.com>]

The device tree binding for st,lis2mdl does not support
st,drdy-int-pin property. However, when no platform data is provided
and the property is absent, the driver falls back to default_magn_pdata
which hardcodes drdy_int_pin = 2. This causes 
`st_sensors_set_drdy_int_pin` to fail with -EINVAL because the LIS2MDL
sensor settings have no INT2 DRDY mask defined.

Fix this by checking the sensor's INT2 DRDY mask availability at
probe time and selecting the appropriate default pin. Sensors that
do not support INT2 DRDY will default to INT1, while all others
retain the existing default of INT2.

Signed-off-by: Advait Dhamorikar <advaitd@mechasystems.com>
---
 drivers/iio/magnetometer/st_magn_core.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/magnetometer/st_magn_core.c b/drivers/iio/magnetometer/st_magn_core.c
index ef348d316c00..64d7edd7b3e1 100644
--- a/drivers/iio/magnetometer/st_magn_core.c
+++ b/drivers/iio/magnetometer/st_magn_core.c
@@ -506,6 +506,11 @@ static const struct st_sensors_platform_data default_magn_pdata = {
 	.drdy_int_pin = 2,
 };
 
+/* LIS2MDL only supports DRDY on INT1 */
+static const struct st_sensors_platform_data alt_magn_pdata = {
+	.drdy_int_pin = 1,
+};
+
 static int st_magn_read_raw(struct iio_dev *indio_dev,
 			struct iio_chan_spec const *ch, int *val,
 							int *val2, long mask)
@@ -628,8 +633,12 @@ int st_magn_common_probe(struct iio_dev *indio_dev)
 	mdata->current_fullscale = &mdata->sensor_settings->fs.fs_avl[0];
 	mdata->odr = mdata->sensor_settings->odr.odr_avl[0].hz;
 
-	if (!pdata)
-		pdata = (struct st_sensors_platform_data *)&default_magn_pdata;
+	if (!pdata) {
+		if (!mdata->sensor_settings->drdy_irq.int2.mask)
+			pdata = (struct st_sensors_platform_data *)&alt_magn_pdata;
+		else
+			pdata = (struct st_sensors_platform_data *)&default_magn_pdata;
+	}
 
 	err = st_sensors_init_sensor(indio_dev, pdata);
 	if (err < 0)
-- 
2.43.0