[PATCH] hwmon: (gpio-fan) allow to use alarm support alone from DT

[simon.guinot@sequanux.org (Simon Guinot)]

On some boards, such as the LaCie 2Big Network v2 or 2Big NAS (based on
Marvell Kirkwood SoCs), an I2C fan controller is used but the alarm
signal is wired to a separate GPIO. Unfortunately, the gpio-fan driver
can't be used to handle GPIO alarm alone from DT: an error is returned
if the "gpios" DT property is missing.

This patch allows to use the gpio-fan driver even if the "alarm-gpios"
DT property is defined alone.

Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
---
 .../devicetree/bindings/gpio/gpio-fan.txt          |  6 ++-
 drivers/hwmon/gpio-fan.c                           | 44 +++++++++++-----------
 2 files changed, 27 insertions(+), 23 deletions(-)

diff --git a/Documentation/devicetree/bindings/gpio/gpio-fan.txt b/Documentation/devicetree/bindings/gpio/gpio-fan.txt
index 2dd457a3469a..a4c5d15b72e6 100644
--- a/Documentation/devicetree/bindings/gpio/gpio-fan.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio-fan.txt
@@ -2,16 +2,18 @@ Bindings for fan connected to GPIO lines
 
 Required properties:
 - compatible : "gpio-fan"
+
+Optional properties:
 - gpios: Specifies the pins that map to bits in the control value,
   ordered MSB-->LSB.
 - gpio-fan,speed-map: A mapping of possible fan RPM speeds and the
   control value that should be set to achieve them. This array
   must have the RPM values in ascending order.
-
-Optional properties:
 - alarm-gpios: This pin going active indicates something is wrong with
   the fan, and a udev event will be fired.
 
+Note: At least one the "gpios" and "alarm-gpios" properties should be set.
+
 Examples:
 
 	gpio_fan {
diff --git a/drivers/hwmon/gpio-fan.c b/drivers/hwmon/gpio-fan.c
index 36abf814b8c7..c241f5b0b7cf 100644
--- a/drivers/hwmon/gpio-fan.c
+++ b/drivers/hwmon/gpio-fan.c
@@ -404,10 +404,32 @@ static int gpio_fan_get_of_pdata(struct device *dev,
 
 	node = dev->of_node;
 
+	/* Alarm GPIO if one exists */
+	if (of_gpio_named_count(node, "alarm-gpios") > 0) {
+		struct gpio_fan_alarm *alarm;
+		int val;
+		enum of_gpio_flags flags;
+
+		alarm = devm_kzalloc(dev, sizeof(struct gpio_fan_alarm),
+					GFP_KERNEL);
+		if (!alarm)
+			return -ENOMEM;
+
+		val = of_get_named_gpio_flags(node, "alarm-gpios", 0, &flags);
+		if (val < 0)
+			return val;
+		alarm->gpio = val;
+		alarm->active_low = flags & OF_GPIO_ACTIVE_LOW;
+
+		pdata->alarm = alarm;
+	}
+
 	/* Fill GPIO pin array */
 	pdata->num_ctrl = of_gpio_count(node);
 	if (pdata->num_ctrl <= 0) {
-		dev_err(dev, "gpios DT property empty / missing");
+		if (pdata->alarm)
+			return 0;
+		dev_err(dev, "DT properties empty / missing");
 		return -ENODEV;
 	}
 	ctrl = devm_kzalloc(dev, pdata->num_ctrl * sizeof(unsigned),
@@ -460,26 +482,6 @@ static int gpio_fan_get_of_pdata(struct device *dev,
 	}
 	pdata->speed = speed;
 
-	/* Alarm GPIO if one exists */
-	if (of_gpio_named_count(node, "alarm-gpios") > 0) {
-		struct gpio_fan_alarm *alarm;
-		int val;
-		enum of_gpio_flags flags;
-
-		alarm = devm_kzalloc(dev, sizeof(struct gpio_fan_alarm),
-					GFP_KERNEL);
-		if (!alarm)
-			return -ENOMEM;
-
-		val = of_get_named_gpio_flags(node, "alarm-gpios", 0, &flags);
-		if (val < 0)
-			return val;
-		alarm->gpio = val;
-		alarm->active_low = flags & OF_GPIO_ACTIVE_LOW;
-
-		pdata->alarm = alarm;
-	}
-
 	return 0;
 }
 
-- 
2.1.1