power: supply: Add sysfs entry for system load control

There are devices that can control the connection from power to system
load. For example, with a field-effect transistor between a battery and
the system load (BATFET). Drivers for these devices are currently
enrolling their own custom `sysfs` property to control this.

In order to unify this, add a new `sysfs` entry for controlling such
switch and corresponding `power_supply_property` with `enum` values. The
obvious states are "on" and "off", i.e. there is a connection or not,
respectively. However, many devices can also enter special modes such as
"low-power", "shipping" or "deep sleep".

Since the members in `struct power_supply_desc` already are ordered,
adding `load_switches` only increases the size with 4 bytes, as can be
seen from `pahole`:

  struct power_supply_desc {
          const char  *              name;                 /*     0     4 */
          enum power_supply_type     type;                 /*     4     4 */
          u32                        charge_types;         /*     8     4 */
          u32                        usb_types;            /*    12     4 */
          u32                        load_switches;        /*    16     4 */
          const enum power_supply_property  * properties;  /*    20     4 */
          size_t                     num_properties;       /*    24     4 */
          int                        (*get_property)(...); /*    28     4 */
          int                        (*set_property)(...); /*    32     4 */
          int                        (*property_is_writeable)(...);  /*    36     4 */
          void                       (*external_power_changed)(...); /*    40     4 */
          int                        (*init)(struct power_supply *); /*    44     4 */
          int                        use_for_apm;          /*    48     4 */
          bool                       no_thermal;           /*    52     1 */
          u8                         charge_behaviours;    /*    53     1 */

          /* size: 56, cachelines: 1, members: 15 */
          /* padding: 2 */
          /* last cacheline: 56 bytes */
  };

Signed-off-by: Waqar Hameed <waqar.hameed@axis.com>
Link: https://patch.msgid.link/d86f528de9a058091f806d9676639239cfeaf805.1788290289.git.waqar.hameed@axis.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/drivers/power/supply/power_supply_sysfs.c b/drivers/power/supply/power_supply_sysfs.c
index 9d6b24856c8b..b0f524d152cf 100644
--- a/drivers/power/supply/power_supply_sysfs.c
+++ b/drivers/power/supply/power_supply_sysfs.c
@@ -152,6 +152,14 @@ static const char * const POWER_SUPPLY_CHARGE_BEHAVIOUR_TEXT[] = {
 	[POWER_SUPPLY_CHARGE_BEHAVIOUR_FORCE_DISCHARGE]		= "force-discharge",
 };
 
+static const char *const POWER_SUPPLY_LOAD_SWITCH_TEXT[] = {
+	[POWER_SUPPLY_LOAD_SWITCH_UNKNOWN] = "Unknown",
+	[POWER_SUPPLY_LOAD_SWITCH_ON]	   = "On",
+	[POWER_SUPPLY_LOAD_SWITCH_OFF]	   = "Off",
+	[POWER_SUPPLY_LOAD_SWITCH_STANDBY] = "Standby",
+	[POWER_SUPPLY_LOAD_SWITCH_SHIP]	   = "Ship",
+};
+
 static struct power_supply_attr power_supply_attrs[] __ro_after_init = {
 	/* Properties of type `int' */
 	POWER_SUPPLY_ENUM_ATTR(STATUS),
@@ -231,6 +239,7 @@ static struct power_supply_attr power_supply_attrs[] __ro_after_init = {
 	POWER_SUPPLY_ATTR(MANUFACTURE_DAY),
 	POWER_SUPPLY_ATTR(INTERNAL_RESISTANCE),
 	POWER_SUPPLY_ATTR(STATE_OF_HEALTH),
+	POWER_SUPPLY_ENUM_ATTR(LOAD_SWITCH),
 	/* Properties of type `const char *' */
 	POWER_SUPPLY_ATTR(MODEL_NAME),
 	POWER_SUPPLY_ATTR(MANUFACTURER),
@@ -400,6 +409,14 @@ static ssize_t power_supply_format_property(struct device *dev,
 		ret = power_supply_show_charge_types(dev, psy,
 						     value.intval, buf);
 		break;
+	case POWER_SUPPLY_PROP_LOAD_SWITCH:
+		if (uevent) /* no possible values in uevents */
+			goto default_format;
+		ret = power_supply_show_enum_with_available(
+			dev, POWER_SUPPLY_LOAD_SWITCH_TEXT,
+			ARRAY_SIZE(POWER_SUPPLY_LOAD_SWITCH_TEXT),
+			psy->desc->load_switches, value.intval, buf);
+		break;
 	case POWER_SUPPLY_PROP_MODEL_NAME ... POWER_SUPPLY_PROP_SERIAL_NUMBER:
 		ret = sysfs_emit(buf, "%s\n", value.strval);
 		break;