[RFC PATCH v2 2/3] hwmon: (adt7475) fan stall prevention

[Chris Packham]

By default adt7475 will stop the fans (pwm duty cycle 0%) when the
temperature drops past Tmin - hysteresis. Some systems want to keep the
fans moving even when the temperature drops so add new sysfs attributes
that configure the enhanced acoustics min 1-3 which allows the fans to
run at the minimum configure pwm duty cycle.

Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
---
Changes in v2:
- use pwmN_stall_dis as the attribute name. I think this describes the purpose
  pretty well. I went with a new attribute instead of overloading
  pwmN_auto_point1_pwm so this doesn't affect existing users.

 Documentation/hwmon/adt7475 |  5 +++++
 drivers/hwmon/adt7475.c     | 50 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/Documentation/hwmon/adt7475 b/Documentation/hwmon/adt7475
index 0502f2b464e1..63507402cd4f 100644
--- a/Documentation/hwmon/adt7475
+++ b/Documentation/hwmon/adt7475
@@ -109,6 +109,11 @@ fan speed) is applied. PWM values range from 0 (off) to 255 (full speed).
 Fan speed may be set to maximum when the temperature sensor associated with
 the PWM control exceeds temp#_max.
 
+At Tmin - hysteresis the PWM output can either be off (0% duty cycle) or at the
+minimum (i.e. auto_point1_pwm). This behaviour be configured using the
+pwm[1-*]_stall_dis sysfs attribute. A value of 0 means the fans will shut off.
+A value of 1 means the fans will run at auto_point1_pwm.
+
 Notes
 -----
 
diff --git a/drivers/hwmon/adt7475.c b/drivers/hwmon/adt7475.c
index ec0c43fbcdce..85957324cd85 100644
--- a/drivers/hwmon/adt7475.c
+++ b/drivers/hwmon/adt7475.c
@@ -79,6 +79,9 @@
 
 #define REG_TEMP_TRANGE_BASE	0x5F
 
+#define REG_ENHANCE_ACOUSTICS1	0x62
+#define REG_ENHANCE_ACOUSTICS2	0x63
+
 #define REG_PWM_MIN_BASE	0x64
 
 #define REG_TEMP_TMIN_BASE	0x67
@@ -209,6 +212,7 @@ struct adt7475_data {
 	u8 range[3];
 	u8 pwmctl[3];
 	u8 pwmchan[3];
+	u8 enh_acou[2];
 
 	u8 vid;
 	u8 vrm;
@@ -700,6 +704,43 @@ static ssize_t set_pwm(struct device *dev, struct device_attribute *attr,
 	data->pwm[sattr->nr][sattr->index] = clamp_val(val, 0, 0xFF);
 	i2c_smbus_write_byte_data(client, reg,
 				  data->pwm[sattr->nr][sattr->index]);
+	mutex_unlock(&data->lock);
+
+	return count;
+}
+
+
+static ssize_t show_stall_dis(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	struct sensor_device_attribute_2 *sattr = to_sensor_dev_attr_2(attr);
+	struct i2c_client *client = to_i2c_client(dev);
+	struct adt7475_data *data = i2c_get_clientdata(client);
+	u8 mask = BIT(5 + sattr->index);
+
+	return sprintf(buf, "%d\n", !!(data->enh_acou[0] & mask));
+}
+
+static ssize_t set_stall_dis(struct device *dev, struct device_attribute *attr,
+			     const char *buf, size_t count)
+{
+	struct sensor_device_attribute_2 *sattr = to_sensor_dev_attr_2(attr);
+	struct i2c_client *client = to_i2c_client(dev);
+	struct adt7475_data *data = i2c_get_clientdata(client);
+	long val;
+	u8 mask = BIT(5 + sattr->index);
+
+	if (kstrtol(buf, 10, &val))
+		return -EINVAL;
+
+	mutex_lock(&data->lock);
+
+	data->enh_acou[0] &= ~mask;
+	if (val)
+		data->enh_acou[0] |= mask;
+
+	i2c_smbus_write_byte_data(client, REG_ENHANCE_ACOUSTICS1,
+				  data->enh_acou[0]);
 
 	mutex_unlock(&data->lock);
 
@@ -1028,6 +1069,8 @@ static SENSOR_DEVICE_ATTR_2(pwm1_auto_point1_pwm, S_IRUGO | S_IWUSR, show_pwm,
 			    set_pwm, MIN, 0);
 static SENSOR_DEVICE_ATTR_2(pwm1_auto_point2_pwm, S_IRUGO | S_IWUSR, show_pwm,
 			    set_pwm, MAX, 0);
+static SENSOR_DEVICE_ATTR_2(pwm1_stall_dis, S_IRUGO | S_IWUSR, show_stall_dis,
+			    set_stall_dis, 0, 0);
 static SENSOR_DEVICE_ATTR_2(pwm2, S_IRUGO | S_IWUSR, show_pwm, set_pwm, INPUT,
 			    1);
 static SENSOR_DEVICE_ATTR_2(pwm2_freq, S_IRUGO | S_IWUSR, show_pwmfreq,
@@ -1040,6 +1083,8 @@ static SENSOR_DEVICE_ATTR_2(pwm2_auto_point1_pwm, S_IRUGO | S_IWUSR, show_pwm,
 			    set_pwm, MIN, 1);
 static SENSOR_DEVICE_ATTR_2(pwm2_auto_point2_pwm, S_IRUGO | S_IWUSR, show_pwm,
 			    set_pwm, MAX, 1);
+static SENSOR_DEVICE_ATTR_2(pwm2_stall_dis, S_IRUGO | S_IWUSR, show_stall_dis,
+			    set_stall_dis, 0, 1);
 static SENSOR_DEVICE_ATTR_2(pwm3, S_IRUGO | S_IWUSR, show_pwm, set_pwm, INPUT,
 			    2);
 static SENSOR_DEVICE_ATTR_2(pwm3_freq, S_IRUGO | S_IWUSR, show_pwmfreq,
@@ -1052,6 +1097,8 @@ static SENSOR_DEVICE_ATTR_2(pwm3_auto_point1_pwm, S_IRUGO | S_IWUSR, show_pwm,
 			    set_pwm, MIN, 2);
 static SENSOR_DEVICE_ATTR_2(pwm3_auto_point2_pwm, S_IRUGO | S_IWUSR, show_pwm,
 			    set_pwm, MAX, 2);
+static SENSOR_DEVICE_ATTR_2(pwm3_stall_dis, S_IRUGO | S_IWUSR, show_stall_dis,
+			    set_stall_dis, 0, 2);
 
 /* Non-standard name, might need revisiting */
 static DEVICE_ATTR_RW(pwm_use_point2_pwm_at_crit);
@@ -1112,12 +1159,14 @@ static struct attribute *adt7475_attrs[] = {
 	&sensor_dev_attr_pwm1_auto_channels_temp.dev_attr.attr,
 	&sensor_dev_attr_pwm1_auto_point1_pwm.dev_attr.attr,
 	&sensor_dev_attr_pwm1_auto_point2_pwm.dev_attr.attr,
+	&sensor_dev_attr_pwm1_stall_dis.dev_attr.attr,
 	&sensor_dev_attr_pwm3.dev_attr.attr,
 	&sensor_dev_attr_pwm3_freq.dev_attr.attr,
 	&sensor_dev_attr_pwm3_enable.dev_attr.attr,
 	&sensor_dev_attr_pwm3_auto_channels_temp.dev_attr.attr,
 	&sensor_dev_attr_pwm3_auto_point1_pwm.dev_attr.attr,
 	&sensor_dev_attr_pwm3_auto_point2_pwm.dev_attr.attr,
+	&sensor_dev_attr_pwm3_stall_dis.dev_attr.attr,
 	&dev_attr_pwm_use_point2_pwm_at_crit.attr,
 	NULL,
 };
@@ -1136,6 +1185,7 @@ static struct attribute *pwm2_attrs[] = {
 	&sensor_dev_attr_pwm2_auto_channels_temp.dev_attr.attr,
 	&sensor_dev_attr_pwm2_auto_point1_pwm.dev_attr.attr,
 	&sensor_dev_attr_pwm2_auto_point2_pwm.dev_attr.attr,
+	&sensor_dev_attr_pwm2_stall_dis.dev_attr.attr,
 	NULL
 };
 
-- 
2.11.0.24.ge6920cf