hwmon: (core) Add support for string attributes to new API

The new API is so far only suited for data attributes and does not work
well for string attributes, specifically for the 'label' attributes.
Provide a separate callback function for those.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/hwmon.c

@@ -178,6 +178,22 @@ static ssize_t hwmon_attr_show(struct device *dev,
 	return sprintf(buf, "%ld\n", val);
 }
 
+static ssize_t hwmon_attr_show_string(struct device *dev,
+				      struct device_attribute *devattr,
+				      char *buf)
+{
+	struct hwmon_device_attribute *hattr = to_hwmon_attr(devattr);
+	char *s;
+	int ret;
+
+	ret = hattr->ops->read_string(dev, hattr->type, hattr->attr,
+				      hattr->index, &s);
+	if (ret < 0)
+		return ret;
+
+	return sprintf(buf, "%s\n", s);
+}
+
 static ssize_t hwmon_attr_store(struct device *dev,
 				struct device_attribute *devattr,
 				const char *buf, size_t count)
@@ -205,6 +221,17 @@ static int hwmon_attr_base(enum hwmon_sensor_types type)
 	return 1;
 }
 
+static bool is_string_attr(enum hwmon_sensor_types type, u32 attr)
+{
+	return (type == hwmon_temp && attr == hwmon_temp_label) ||
+	       (type == hwmon_in && attr == hwmon_in_label) ||
+	       (type == hwmon_curr && attr == hwmon_curr_label) ||
+	       (type == hwmon_power && attr == hwmon_power_label) ||
+	       (type == hwmon_energy && attr == hwmon_energy_label) ||
+	       (type == hwmon_humidity && attr == hwmon_humidity_label) ||
+	       (type == hwmon_fan && attr == hwmon_fan_label);
+}
+
 static struct attribute *hwmon_genattr(struct device *dev,
 				       const void *drvdata,
 				       enum hwmon_sensor_types type,
@@ -218,6 +245,7 @@ static struct attribute *hwmon_genattr(struct device *dev,
 	struct attribute *a;
 	umode_t mode;
 	char *name;
+	bool is_string = is_string_attr(type, attr);
 
 	/* The attribute is invisible if there is no template string */
 	if (!template)
@@ -227,7 +255,8 @@ static struct attribute *hwmon_genattr(struct device *dev,
 	if (!mode)
 		return ERR_PTR(-ENOENT);
 
-	if ((mode & S_IRUGO) && !ops->read)
+	if ((mode & S_IRUGO) && ((is_string && !ops->read_string) ||
+				 (!is_string && !ops->read)))
 		return ERR_PTR(-EINVAL);
 	if ((mode & S_IWUGO) && !ops->write)
 		return ERR_PTR(-EINVAL);
@@ -252,7 +281,7 @@ static struct attribute *hwmon_genattr(struct device *dev,
 	hattr->ops = ops;
 
 	dattr = &hattr->dev_attr;
-	dattr->show = hwmon_attr_show;
+	dattr->show = is_string ? hwmon_attr_show_string : hwmon_attr_show;
 	dattr->store = hwmon_attr_store;
 
 	a = &dattr->attr;

include/linux/hwmon.h

@@ -298,7 +298,8 @@ enum hwmon_pwm_attributes {
  *			Channel number
  *		The function returns the file permissions.
  *		If the return value is 0, no attribute will be created.
- * @read:	Read callback. Mandatory if readable attributes are present.
+ * @read:	Read callback for data attributes. Mandatory if readable
+ *		data attributes are present.
  *		Parameters are:
  *		@dev:	Pointer to hardware monitoring device
  *		@type:	Sensor type
@@ -307,7 +308,19 @@ enum hwmon_pwm_attributes {
  *			Channel number
  *		@val:	Pointer to returned value
  *		The function returns 0 on success or a negative error number.
- * @write:	Write callback. Mandatory if writeable attributes are present.
+ * @read_string:
+ *		Read callback for string attributes. Mandatory if string
+ *		attributes are present.
+ *		Parameters are:
+ *		@dev:	Pointer to hardware monitoring device
+ *		@type:	Sensor type
+ *		@attr:	Sensor attribute
+ *		@channel:
+ *			Channel number
+ *		@str:	Pointer to returned string
+ *		The function returns 0 on success or a negative error number.
+ * @write:	Write callback for data attributes. Mandatory if writeable
+ *		data attributes are present.
  *		Parameters are:
  *		@dev:	Pointer to hardware monitoring device
  *		@type:	Sensor type
@@ -322,6 +335,8 @@ struct hwmon_ops {
 			      u32 attr, int channel);
 	int (*read)(struct device *dev, enum hwmon_sensor_types type,
 		    u32 attr, int channel, long *val);
+	int (*read_string)(struct device *dev, enum hwmon_sensor_types type,
+		    u32 attr, int channel, char **str);
 	int (*write)(struct device *dev, enum hwmon_sensor_types type,
 		     u32 attr, int channel, long val);
 };