power_supply: add SCOPE attribute to power supplies

This adds a "scope" attribute to a power_supply, which indicates how
much of the system it powers.  It appears in sysfs as "scope" or in
the uevent file as POWER_SUPPLY_SCOPE=.  There are presently three
possible values:
	Unknown - unknown power topology
	System - the power supply powers the whole system
	Device - it powers a specific device, or tree of devices

A power supply which doesn't have a "scope" attribute should be assumed to
have "System" scope.

In general, usermode should assume that loss of all System-scoped power
supplies will power off the whole system, but any single one is sufficient
to power the system.

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Richard Hughes <richard@hughsie.com>

drivers/power/power_supply_sysfs.c

@@ -63,6 +63,9 @@ static ssize_t power_supply_show_property(struct device *dev,
 	static char *capacity_level_text[] = {
 		"Unknown", "Critical", "Low", "Normal", "High", "Full"
 	};
+	static char *scope_text[] = {
+		"Unknown", "System", "Device"
+	};
 	ssize_t ret = 0;
 	struct power_supply *psy = dev_get_drvdata(dev);
 	const ptrdiff_t off = attr - power_supply_attrs;
@@ -95,6 +98,8 @@ static ssize_t power_supply_show_property(struct device *dev,
 		return sprintf(buf, "%s\n", capacity_level_text[value.intval]);
 	else if (off == POWER_SUPPLY_PROP_TYPE)
 		return sprintf(buf, "%s\n", type_text[value.intval]);
+	else if (off == POWER_SUPPLY_PROP_SCOPE)
+		return sprintf(buf, "%s\n", scope_text[value.intval]);
 	else if (off >= POWER_SUPPLY_PROP_MODEL_NAME)
 		return sprintf(buf, "%s\n", value.strval);
 
@@ -167,6 +172,7 @@ static struct device_attribute power_supply_attrs[] = {
 	POWER_SUPPLY_ATTR(time_to_full_now),
 	POWER_SUPPLY_ATTR(time_to_full_avg),
 	POWER_SUPPLY_ATTR(type),
+	POWER_SUPPLY_ATTR(scope),
 	/* Properties of type `const char *' */
 	POWER_SUPPLY_ATTR(model_name),
 	POWER_SUPPLY_ATTR(manufacturer),