[PATCH v2 4/4] iio: proximity: rfd77402: Add interrupt handling support

[Shrikant Raskar <raskar.shree97@gmail.com>]

Add interrupt handling support to enable event-driven data acquisition
instead of continuous polling. This improves responsiveness, reduces
CPU overhead, and supports low-power operation by allowing the system
to remain idle until an interrupt occurs.

Signed-off-by: Shrikant Raskar <raskar.shree97@gmail.com>
---
Changelog:
Changes since v1:
- Remove 'of.h' header
- Split the condition in 2 parts in interrupt handler
- Add helper rfd77402_wait_for_irq()
- Add helper rfd77402_config_irq()
- Code refactoring
- Return failure if request IRQ failed

Link to v1:https://lore.kernel.org/all/20251126031440.30065-4-raskar.shree97@gmail.com/

Test Logs:
1. Interrupt Mode :
pi@raspberrypi:~$ sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- UU -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         
pi@raspberrypi:~$ cat /sys/bus/iio/devices/iio:device0/in_distance_raw
35
pi@raspberrypi:~$ cat /sys/bus/iio/devices/iio:device0/in_distance_raw
39
pi@raspberrypi:~$ cat /proc/interrupts | grep rfd
127:          2          0          0          0 pinctrl-bcm2835   4 Edge      rfd77402
pi@raspberrypi:~$ dmesg | grep rfd
[    7.464789] rfd77402 1-004c: Using interrupt mode

2. Polling Mode :
pi@raspberrypi:~$ sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- UU -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         
pi@raspberrypi:~$ dmesg | grep rfd
[   26.908031] rfd77402 1-004c: No interrupt specified, using polling mode
pi@raspberrypi:~$ cat /sys/bus/iio/devices/iio:device0/in_distance_raw
36
pi@raspberrypi:~$ cat /sys/bus/iio/devices/iio:device0/in_distance_raw
45
---
 drivers/iio/proximity/rfd77402.c | 126 +++++++++++++++++++++++++++++--
 1 file changed, 118 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/proximity/rfd77402.c b/drivers/iio/proximity/rfd77402.c
index 2152509816ca..8441a7bcabec 100644
--- a/drivers/iio/proximity/rfd77402.c
+++ b/drivers/iio/proximity/rfd77402.c
@@ -6,19 +6,21 @@
  *
  * 7-bit I2C slave address 0x4c
  *
- * TODO: interrupt
  * https://media.digikey.com/pdf/Data%20Sheets/RF%20Digital%20PDFs/RFD77402.pdf
  */
 
 #include <linux/module.h>
 #include <linux/i2c.h>
 #include <linux/delay.h>
-
+#include <linux/interrupt.h>
+#include <linux/completion.h>
 #include <linux/iio/iio.h>
 
 #define RFD77402_DRV_NAME "rfd77402"
 
 #define RFD77402_ICSR		0x00 /* Interrupt Control Status Register */
+#define RFD77402_ICSR_CLR_CFG   BIT(0)
+#define RFD77402_ICSR_CLR_TYPE  BIT(1)
 #define RFD77402_ICSR_INT_MODE	BIT(2)
 #define RFD77402_ICSR_INT_POL	BIT(3)
 #define RFD77402_ICSR_RESULT	BIT(4)
@@ -26,6 +28,12 @@
 #define RFD77402_ICSR_H2M_MSG	BIT(6)
 #define RFD77402_ICSR_RESET	BIT(7)
 
+#define RFD77402_IER		0x02
+#define RFD77402_IER_RESULT	BIT(0)
+#define RFD77402_IER_M2H_MSG	BIT(1)
+#define RFD77402_IER_H2M_MSG	BIT(2)
+#define RFD77402_IER_RESET	BIT(3)
+
 #define RFD77402_CMD_R		0x04
 #define RFD77402_CMD_SINGLE	0x01
 #define RFD77402_CMD_STANDBY	0x10
@@ -80,6 +88,10 @@ struct rfd77402_data {
 	struct i2c_client *client;
 	/* Serialize reads from the sensor */
 	struct mutex lock;
+	/* Completion for interrupt-driven measurements */
+	struct completion completion;
+	/* Flag to indicate if interrupt is available */
+	bool irq_en;
 };
 
 static const struct iio_chan_spec rfd77402_channels[] = {
@@ -110,6 +122,36 @@ static int rfd77402_set_state(struct i2c_client *client, u8 state, u16 check)
 	return 0;
 }
 
+static irqreturn_t rfd77402_interrupt_handler(int irq, void *dev_id)
+{
+	struct rfd77402_data *data = dev_id;
+	int ret;
+
+	ret = i2c_smbus_read_byte_data(data->client, RFD77402_ICSR);
+	if (ret < 0)
+		return IRQ_NONE;
+
+	/* Check if the interrupt is from our device */
+	if (!(ret & RFD77402_ICSR_RESULT))
+		return IRQ_NONE;
+
+	/* Signal completion of measurement */
+	complete(&data->completion);
+	return IRQ_HANDLED;
+}
+
+static int rfd77402_wait_for_irq(struct rfd77402_data *data)
+{
+	int ret;
+
+	ret = wait_for_completion_timeout(&data->completion,
+					  msecs_to_jiffies(200));
+	if (ret == 0)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
 static int rfd77402_result_polling(struct i2c_client *client)
 {
 	int ret;
@@ -129,21 +171,31 @@ static int rfd77402_result_polling(struct i2c_client *client)
 	return -ETIMEDOUT;
 }
 
-static int rfd77402_measure(struct i2c_client *client)
+static int rfd77402_measure(struct rfd77402_data *data)
 {
+	struct i2c_client *client = data->client;
 	int ret;
+
 	ret = rfd77402_set_state(client, RFD77402_CMD_MCPU_ON,
 				 RFD77402_STATUS_MCPU_ON);
 	if (ret < 0)
 		return ret;
 
+	/* Initialize completion for interrupt mode */
+	if (data->irq_en)
+		reinit_completion(&data->completion);
+
 	ret = i2c_smbus_write_byte_data(client, RFD77402_CMD_R,
 					RFD77402_CMD_SINGLE |
 					RFD77402_CMD_VALID);
 	if (ret < 0)
 		goto err;
 		
-	ret = rfd77402_result_polling(client);
+	if (data->irq_en)
+		ret = rfd77402_wait_for_irq(data);
+	else
+		ret = rfd77402_result_polling(data->client);
+
 	if (ret < 0)
 		goto err;
 
@@ -175,7 +227,7 @@ static int rfd77402_read_raw(struct iio_dev *indio_dev,
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
 		mutex_lock(&data->lock);
-		ret = rfd77402_measure(data->client);
+		ret = rfd77402_measure(data);
 		mutex_unlock(&data->lock);
 		if (ret < 0)
 			return ret;
@@ -195,8 +247,25 @@ static const struct iio_info rfd77402_info = {
 	.read_raw = rfd77402_read_raw,
 };
 
+static int rfd77402_config_irq(struct i2c_client *client, u8 csr, u8 ier)
+{
+	int ret;
+
+	ret = i2c_smbus_write_byte_data(client, RFD77402_ICSR, csr);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_write_byte_data(client, RFD77402_IER, ier);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
 static int rfd77402_init(struct i2c_client *client)
 {
+	struct iio_dev *indio_dev = i2c_get_clientdata(client);
+	struct rfd77402_data *data = iio_priv(indio_dev);
 	int ret, i;
 
 	ret = rfd77402_set_state(client, RFD77402_CMD_STANDBY,
@@ -204,9 +273,25 @@ static int rfd77402_init(struct i2c_client *client)
 	if (ret < 0)
 		return ret;
 
-	/* configure INT pad as push-pull, active low */
-	ret = i2c_smbus_write_byte_data(client, RFD77402_ICSR,
-					RFD77402_ICSR_INT_MODE);
+	if (data->irq_en) {
+	/*
+	 * Enable interrupt mode:
+	 * - Configure ICSR for auto-clear on read, push-pull output and falling edge
+	 * - Enable "result ready" interrupt in IER
+	 */
+		ret = rfd77402_config_irq(client,
+					  RFD77402_ICSR_CLR_CFG |
+					  RFD77402_ICSR_INT_MODE,
+					  RFD77402_IER_RESULT);
+	} else {
+	/*
+	 * Disable all interrupts:
+	 * - Clear ICSR configuration
+	 * - Disable all interrupt in IER
+	 */
+		ret = rfd77402_config_irq(client, 0, 0);
+	}
+
 	if (ret < 0)
 		return ret;
 
@@ -283,6 +368,31 @@ static int rfd77402_probe(struct i2c_client *client)
 	data = iio_priv(indio_dev);
 	data->client = client;
 	mutex_init(&data->lock);
+	init_completion(&data->completion);
+
+	i2c_set_clientdata(client, indio_dev);
+
+	data->irq_en = false;
+	if (client->irq > 0) {
+		/* interrupt mode */
+		ret = devm_request_threaded_irq(&client->dev, client->irq,
+						NULL, rfd77402_interrupt_handler,
+						IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
+						"rfd77402", data);
+		if (ret < 0) {
+			dev_err(&client->dev,
+				"Failed to request IRQ %d: %d\n",
+				client->irq, ret);
+			return ret;
+		}
+
+		data->irq_en = true;
+		dev_info(&client->dev, "Using interrupt mode\n");
+
+	} else {
+		/* polling mode */
+		dev_info(&client->dev, "No interrupt specified, using polling mode\n");
+	}
 
 	indio_dev->info = &rfd77402_info;
 	indio_dev->channels = rfd77402_channels;
-- 
2.43.0