iio: humidity: hts221: support open drain mode

Add open drain support in order to share requested IRQ line between
hts221 device and other peripherals

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/humidity/hts221_buffer.c

@@ -20,10 +20,14 @@
 #include <linux/iio/triggered_buffer.h>
 #include <linux/iio/buffer.h>
 
+#include <linux/platform_data/st_sensors_pdata.h>
+
 #include "hts221.h"
 
 #define HTS221_REG_DRDY_HL_ADDR		0x22
 #define HTS221_REG_DRDY_HL_MASK		BIT(7)
+#define HTS221_REG_DRDY_PP_OD_ADDR	0x22
+#define HTS221_REG_DRDY_PP_OD_MASK	BIT(6)
 #define HTS221_REG_STATUS_ADDR		0x27
 #define HTS221_RH_DRDY_MASK		BIT(1)
 #define HTS221_TEMP_DRDY_MASK		BIT(0)
@@ -69,7 +73,9 @@ static irqreturn_t hts221_trigger_handler_thread(int irq, void *private)
 int hts221_allocate_trigger(struct hts221_hw *hw)
 {
 	struct iio_dev *iio_dev = iio_priv_to_dev(hw);
-	bool irq_active_low = false;
+	bool irq_active_low = false, open_drain = false;
+	struct device_node *np = hw->dev->of_node;
+	struct st_sensors_platform_data *pdata;
 	unsigned long irq_type;
 	int err;
 
@@ -95,6 +101,20 @@ int hts221_allocate_trigger(struct hts221_hw *hw)
 				     HTS221_REG_DRDY_HL_MASK, irq_active_low);
 	if (err < 0)
 		return err;
+
+	pdata = (struct st_sensors_platform_data *)hw->dev->platform_data;
+	if ((np && of_property_read_bool(np, "drive-open-drain")) ||
+	    (pdata && pdata->open_drain)) {
+		irq_type |= IRQF_SHARED;
+		open_drain = true;
+	}
+
+	err = hts221_write_with_mask(hw, HTS221_REG_DRDY_PP_OD_ADDR,
+				     HTS221_REG_DRDY_PP_OD_MASK,
+				     open_drain);
+	if (err < 0)
+		return err;
+
 	err = devm_request_threaded_irq(hw->dev, hw->irq, NULL,
 					hts221_trigger_handler_thread,
 					irq_type | IRQF_ONESHOT,