i2c: support gpio-binding for SMBAlerts

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 <[e-mail]>
Reviewed-by: Andi Shyti <[e-mail]>

drivers/i2c/i2c-core-smbus.c

···
 	if (!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));
 }

drivers/i2c/i2c-smbus.c

···
 
 #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>
···
 	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),
···
 	} 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;
 	}