Date:	Tue, 16 Aug 2016 09:53:54 +0200
From:	Mike Looijmans <mike.looijmans@...ic.nl>
To:	linux-hwmon@...r.kernel.org, linux@...ck-us.net
Cc:	linux-kernel@...r.kernel.org,
	Mike Looijmans <mike.looijmans@...ic.nl>
Subject: [PATCH] hwmon: (max6650) Allow fan shutdown and a more intuitive mode interface

The fan can be stopped by writing "0" to fan1_target in sysfs.

Writing non-zero values to fan1_target or pwm1 in sysfs automatically
selects the corresponding control mode (closed or open loop).

This allows userspace applications to control the fan speed without
the need to know specific details of the controller (like the fact
that fan1_target does not take effect when pwm1_enable is set to
anything but "2"). Early initialization of the fan controller prevents
overheating, for example when resetting the board while the fan was
completely turned off.

Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>
---
This patch requires the devicetree support patch for the max6650.

Changes the functionality and interface of the driver, to be able to
initialize the chip at boot, and allows userspace control without
requiring hardware knowledge.

 .../devicetree/bindings/hwmon/max6650.txt          |   5 +
 Documentation/hwmon/max6650                        |   5 +-
 drivers/hwmon/max6650.c                            | 153 +++++++++++++--------
 3 files changed, 106 insertions(+), 57 deletions(-)

diff --git a/Documentation/devicetree/bindings/hwmon/max6650.txt b/Documentation/devicetree/bindings/hwmon/max6650.txt
index 2e46e69..724ab3a 100644
--- a/Documentation/devicetree/bindings/hwmon/max6650.txt
+++ b/Documentation/devicetree/bindings/hwmon/max6650.txt
@@ -13,6 +13,10 @@ Optional properties, default is to retain the chip's current setting:
 - maxim,fan-prescale  : Pre-scaling value, as per datasheet [1]. Lower values
 			allow more fine-grained control of slower fans.
 			Valid: 1, 2, 4, 8, 16.
+- maxim,fan-target-rpm: Initial requested fan rotation speed. If specified, the
+			driver selects closed-loop mode and the requested speed.
+			This ensures the fan is already running before userspace
+			takes over.
 
 Example:
 	fan-max6650: max6650@1b {
@@ -20,4 +24,5 @@ Example:
 		compatible = "maxim,max6650";
 		maxim,fan-microvolt = <12000000>;
 		maxim,fan-prescale = <4>;
+		maxim,fan-target-rpm = <1200>;
 	};
diff --git a/Documentation/hwmon/max6650 b/Documentation/hwmon/max6650
index 58d9644..53e308b 100644
--- a/Documentation/hwmon/max6650
+++ b/Documentation/hwmon/max6650
@@ -33,9 +33,12 @@ fan2_input	ro	"
 fan3_input	ro	"
 fan4_input	ro	"
 fan1_target	rw	desired fan speed in RPM (closed loop mode only)
+			Set to 0 to stop the fan. Writing any other value sets
+			the regulator mode to "closed loop".
 pwm1_enable	rw	regulator mode, 0=full on, 1=open loop, 2=closed loop
 pwm1		rw	relative speed (0-255), 255=max. speed.
-			Used in open loop mode only.
+			Set to 0 to stop the fan. Writing any other value sets
+			the regulator mode to "open loop".
 fan1_div	rw	sets the speed range the inputs can handle. Legal
 			values are 1, 2, 4, and 8. Use lower values for
 			faster fans.
diff --git a/drivers/hwmon/max6650.c b/drivers/hwmon/max6650.c
index 6beb62c..d40756a 100644
--- a/drivers/hwmon/max6650.c
+++ b/drivers/hwmon/max6650.c
@@ -185,6 +185,35 @@ static struct max6650_data *max6650_update_device(struct device *dev)
 	return data;
 }
 
+static bool max6650_is_powerdown(const struct max6650_data *data)
+{
+	return (data->config & MAX6650_CFG_MODE_MASK) == MAX6650_CFG_MODE_OFF;
+}
+
+/*
+ * Change the operating mode of the chip (if needed).
+ * mode is one of the MAX6650_CFG_MODE_* values.
+ */
+static int max6650_set_operating_mode(struct max6650_data *data, u8 mode)
+{
+	int result;
+	u8 config = data->config;
+
+	if (mode == (config & MAX6650_CFG_MODE_MASK))
+		return 0;
+
+	config = (config & ~MAX6650_CFG_MODE_MASK) | mode;
+
+	result = i2c_smbus_write_byte_data(data->client, MAX6650_REG_CONFIG,
+					   config);
+	if (result < 0)
+		return result;
+
+	data->config = config;
+
+	return 0;
+}
+
 static ssize_t get_fan(struct device *dev, struct device_attribute *devattr,
 		       char *buf)
 {
@@ -258,26 +287,26 @@ static ssize_t get_target(struct device *dev, struct device_attribute *devattr,
 	 *    FanSpeed = KSCALE x fCLK / [256 x (KTACH + 1)]
 	 *
 	 * then multiply by 60 to give rpm.
+	 *
+	 * When not running, report target to be "0".
 	 */
 
-	kscale = DIV_FROM_REG(data->config);
-	ktach = data->speed;
-	rpm = 60 * kscale * clock / (256 * (ktach + 1));
+	if (max6650_is_powerdown(data))
+		rpm = 0;
+	else {
+		kscale = DIV_FROM_REG(data->config);
+		ktach = data->speed;
+		rpm = 60 * kscale * clock / (256 * (ktach + 1));
+	}
 	return sprintf(buf, "%d\n", rpm);
 }
 
-static ssize_t set_target(struct device *dev, struct device_attribute *devattr,
-			 const char *buf, size_t count)
+static int max6650_set_target(struct max6650_data *data, unsigned long rpm)
 {
-	struct max6650_data *data = dev_get_drvdata(dev);
-	struct i2c_client *client = data->client;
 	int kscale, ktach;
-	unsigned long rpm;
-	int err;
 
-	err = kstrtoul(buf, 10, &rpm);
-	if (err)
-		return err;
+	if (rpm == 0)
+		return max6650_set_operating_mode(data, MAX6650_CFG_MODE_OFF);
 
 	rpm = clamp_val(rpm, FAN_RPM_MIN, FAN_RPM_MAX);
 
@@ -288,8 +317,6 @@ static ssize_t set_target(struct device *dev, struct device_attribute *devattr,
 	 *     KTACH = [(fCLK x KSCALE) / (256 x FanSpeed)] - 1
 	 */
 
-	mutex_lock(&data->update_lock);
-
 	kscale = DIV_FROM_REG(data->config);
 	ktach = ((clock * kscale) / (256 * rpm / 60)) - 1;
 	if (ktach < 0)
@@ -298,7 +325,25 @@ static ssize_t set_target(struct device *dev, struct device_attribute *devattr,
 		ktach = 255;
 	data->speed = ktach;
 
-	i2c_smbus_write_byte_data(client, MAX6650_REG_SPEED, data->speed);
+	i2c_smbus_write_byte_data(data->client, MAX6650_REG_SPEED, data->speed);
+
+	return max6650_set_operating_mode(data, MAX6650_CFG_MODE_CLOSED_LOOP);
+}
+
+static ssize_t set_target(struct device *dev, struct device_attribute *devattr,
+			 const char *buf, size_t count)
+{
+	struct max6650_data *data = dev_get_drvdata(dev);
+	unsigned long rpm;
+	int err;
+
+	err = kstrtoul(buf, 10, &rpm);
+	if (err)
+		return err;
+
+	mutex_lock(&data->update_lock);
+
+	err = max6650_set_target(data, rpm);
 
 	mutex_unlock(&data->update_lock);
 
@@ -320,17 +365,21 @@ static ssize_t get_pwm(struct device *dev, struct device_attribute *devattr,
 	int pwm;
 	struct max6650_data *data = max6650_update_device(dev);
 
-	/*
-	 * Useful range for dac is 0-180 for 12V fans and 0-76 for 5V fans.
-	 * Lower DAC values mean higher speeds.
-	 */
-	if (data->config & MAX6650_CFG_V12)
-		pwm = 255 - (255 * (int)data->dac)/180;
-	else
-		pwm = 255 - (255 * (int)data->dac)/76;
-
-	if (pwm < 0)
+	if (max6650_is_powerdown(data))
 		pwm = 0;
+	else {
+		/*
+		 * Useful range for dac is 0-180 for 12V fans and 0-76 for 5V
+		 * fans. Lower DAC values mean higher speeds.
+		 */
+		if (data->config & MAX6650_CFG_V12)
+			pwm = 255 - (255 * (int)data->dac)/180;
+		else
+			pwm = 255 - (255 * (int)data->dac)/76;
+
+		if (pwm < 0)
+			pwm = 0;
+	}
 
 	return sprintf(buf, "%d\n", pwm);
 }
@@ -351,16 +400,20 @@ static ssize_t set_pwm(struct device *dev, struct device_attribute *devattr,
 
 	mutex_lock(&data->update_lock);
 
-	if (data->config & MAX6650_CFG_V12)
-		data->dac = 180 - (180 * pwm)/255;
-	else
-		data->dac = 76 - (76 * pwm)/255;
-
-	i2c_smbus_write_byte_data(client, MAX6650_REG_DAC, data->dac);
+	if (pwm == 0)
+		err = max6650_set_operating_mode(data, MAX6650_CFG_MODE_OFF);
+	else {
+		if (data->config & MAX6650_CFG_V12)
+			data->dac = 180 - (180 * pwm)/255;
+		else
+			data->dac = 76 - (76 * pwm)/255;
+		i2c_smbus_write_byte_data(client, MAX6650_REG_DAC, data->dac);
+		err = max6650_set_operating_mode(data, MAX6650_CFG_MODE_OPEN_LOOP);
+	}
 
 	mutex_unlock(&data->update_lock);
 
-	return count;
+	return err < 0 ? err : count;
 }
 
 /*
@@ -385,25 +438,24 @@ static ssize_t set_enable(struct device *dev, struct device_attribute *devattr,
 			  const char *buf, size_t count)
 {
 	struct max6650_data *data = dev_get_drvdata(dev);
-	struct i2c_client *client = data->client;
-	int max6650_modes[3] = {0, 3, 2};
 	unsigned long mode;
 	int err;
+	const u8 max6650_modes[3] = {
+		MAX6650_CFG_MODE_ON,
+		MAX6650_CFG_MODE_OPEN_LOOP,
+		MAX6650_CFG_MODE_CLOSED_LOOP
+		};
 
 	err = kstrtoul(buf, 10, &mode);
 	if (err)
 		return err;
 
-	if (mode > 2)
+	if (mode >= ARRAY_SIZE(max6650_modes))
 		return -EINVAL;
 
 	mutex_lock(&data->update_lock);
 
-	data->config = i2c_smbus_read_byte_data(client, MAX6650_REG_CONFIG);
-	data->config = (data->config & ~MAX6650_CFG_MODE_MASK)
-		       | (max6650_modes[mode] << 4);
-
-	i2c_smbus_write_byte_data(client, MAX6650_REG_CONFIG, data->config);
+	max6650_set_operating_mode(data, max6650_modes[mode]);
 
 	mutex_unlock(&data->update_lock);
 
@@ -582,6 +634,7 @@ static int max6650_init_client(struct max6650_data *data,
 	int err = -EIO;
 	u32 voltage;
 	u32 prescale;
+	u32 target_rpm;
 
 	if (of_property_read_u32(dev->of_node, "maxim,fan-microvolt",
 				 &voltage))
@@ -642,22 +695,6 @@ static int max6650_init_client(struct max6650_data *data,
 		 (config & MAX6650_CFG_V12) ? 12 : 5,
 		 1 << (config & MAX6650_CFG_PRESCALER_MASK));
 
-	/*
-	 * If mode is set to "full off", we change it to "open loop" and
-	 * set DAC to 255, which has the same effect. We do this because
-	 * there's no "full off" mode defined in hwmon specifications.
-	 */
-
-	if ((config & MAX6650_CFG_MODE_MASK) == MAX6650_CFG_MODE_OFF) {
-		dev_dbg(dev, "Change mode to open loop, full off.\n");
-		config = (config & ~MAX6650_CFG_MODE_MASK)
-			 | MAX6650_CFG_MODE_OPEN_LOOP;
-		if (i2c_smbus_write_byte_data(client, MAX6650_REG_DAC, 255)) {
-			dev_err(dev, "DAC write error, aborting.\n");
-			return err;
-		}
-	}
-
 	if (i2c_smbus_write_byte_data(client, MAX6650_REG_CONFIG, config)) {
 		dev_err(dev, "Config write error, aborting.\n");
 		return err;
@@ -666,6 +703,10 @@ static int max6650_init_client(struct max6650_data *data,
 	data->config = config;
 	data->count = i2c_smbus_read_byte_data(client, MAX6650_REG_COUNT);
 
+	if (!of_property_read_u32(client->dev.of_node, "maxim,fan-target-rpm",
+				 &target_rpm))
+		max6650_set_target(data, target_rpm);
+
 	return 0;
 }
 
-- 
1.9.1

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