[PATCH] i2c: support gpio-binding for SMBAlerts

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

Most I2C controllers do not have a dedicated pin for SMBus Alerts. Allow
them to define a GPIO as a side-channel.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
---

The binding addition for dt-schema is here:
https://lore.kernel.org/r/20240909105835.28531-1-wsa+renesas@sang-engineering.com

Tested with a Renesas Lager board (R-Car H2).

 drivers/i2c/i2c-core-smbus.c |  9 ++++++---
 drivers/i2c/i2c-smbus.c      | 22 ++++++++++++++++------
 2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/drivers/i2c/i2c-core-smbus.c b/drivers/i2c/i2c-core-smbus.c
index 967bd712c638..fb3d4674be0c 100644
--- a/drivers/i2c/i2c-core-smbus.c
+++ b/drivers/i2c/i2c-core-smbus.c
@@ -712,12 +712,15 @@ int i2c_setup_smbus_alert(struct i2c_adapter *adapter)
 	if (!parent || i2c_verify_adapter(parent))
 		return 0;
 
+	/* Report serious errors */
 	irq = device_property_match_string(parent, "interrupt-names", "smbus_alert");
-	if (irq == -EINVAL || irq == -ENODATA)
-		return 0;
-	else if (irq < 0)
+	if (irq < 0 && irq != -EINVAL && irq != -ENODATA)
 		return irq;
 
+	/* Skip setup when no irq was found */
+	if (irq < 0 && !device_property_present(parent, "smbalert-gpios"))
+		return 0;
+
 	return PTR_ERR_OR_ZERO(i2c_new_smbus_alert_device(adapter, NULL));
 }
 #endif
diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index bf23e3446123..10198e5efb50 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/drivers/i2c/i2c-smbus.c
@@ -9,6 +9,7 @@
 #define DEBUG
 #include <linux/device.h>
 #include <linux/dmi.h>
+#include <linux/gpio/consumer.h>
 #include <linux/i2c.h>
 #include <linux/i2c-smbus.h>
 #include <linux/interrupt.h>
@@ -168,6 +169,8 @@ static int smbalert_probe(struct i2c_client *ara)
 	struct i2c_smbus_alert_setup *setup = dev_get_platdata(&ara->dev);
 	struct i2c_smbus_alert *alert;
 	struct i2c_adapter *adapter = ara->adapter;
+	unsigned long irqflags = IRQF_SHARED | IRQF_ONESHOT;
+	struct gpio_desc *gpiod;
 	int res, irq;
 
 	alert = devm_kzalloc(&ara->dev, sizeof(struct i2c_smbus_alert),
@@ -180,18 +183,25 @@ static int smbalert_probe(struct i2c_client *ara)
 	} else {
 		irq = fwnode_irq_get_byname(dev_fwnode(adapter->dev.parent),
 					    "smbus_alert");
-		if (irq <= 0)
-			return irq;
+		if (irq <= 0) {
+			gpiod = devm_gpiod_get(adapter->dev.parent, "smbalert", GPIOD_IN);
+			if (IS_ERR(gpiod))
+				return PTR_ERR(gpiod);
+
+			irq = gpiod_to_irq(gpiod);
+			if (irq <= 0)
+				return irq;
+
+			irqflags |= IRQF_TRIGGER_FALLING;
+		}
 	}
 
 	INIT_WORK(&alert->alert, smbalert_work);
 	alert->ara = ara;
 
 	if (irq > 0) {
-		res = devm_request_threaded_irq(&ara->dev, irq,
-						NULL, smbus_alert,
-						IRQF_SHARED | IRQF_ONESHOT,
-						"smbus_alert", alert);
+		res = devm_request_threaded_irq(&ara->dev, irq, NULL, smbus_alert,
+						irqflags, "smbus_alert", alert);
 		if (res)
 			return res;
 	}
-- 
2.43.0