usb: common: usb-conn-gpio: Register charger

Register a power supply charger, whose online state depends on whether
the USB role is set to device or not.

This is useful when the USB role is the only way to know if the device
is charging from USB. The API is the standard power supply charger API,
you get a /sys/class/power_supply/xxx/online node which tells you the
state of the charger.

The sole purpose of this is to give userspace applications a way to
know whether or not the charger is plugged.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20200727170413.23131-1-paul@crapouillou.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/common/Kconfig

@@ -40,6 +40,7 @@ config USB_CONN_GPIO
 	tristate "USB GPIO Based Connection Detection Driver"
 	depends on GPIOLIB
 	select USB_ROLE_SWITCH
+	select POWER_SUPPLY
 	help
 	  The driver supports USB role switch between host and device via GPIO
 	  based USB cable detection, used typically if an input GPIO is used

drivers/usb/common/usb-conn-gpio.c

@@ -17,6 +17,7 @@
 #include <linux/of.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/platform_device.h>
+#include <linux/power_supply.h>
 #include <linux/regulator/consumer.h>
 #include <linux/usb/role.h>
 
@@ -38,6 +39,9 @@ struct usb_conn_info {
 	struct gpio_desc *vbus_gpiod;
 	int id_irq;
 	int vbus_irq;
+
+	struct power_supply_desc desc;
+	struct power_supply *charger;
 };
 
 /*
@@ -104,6 +108,8 @@ static void usb_conn_detect_cable(struct work_struct *work)
 
 	dev_dbg(info->dev, "vbus regulator is %s\n",
 		regulator_is_enabled(info->vbus) ? "enabled" : "disabled");
+
+	power_supply_changed(info->charger);
 }
 
 static void usb_conn_queue_dwork(struct usb_conn_info *info,
@@ -121,10 +127,35 @@ static irqreturn_t usb_conn_isr(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+static enum power_supply_property usb_charger_properties[] = {
+	POWER_SUPPLY_PROP_ONLINE,
+};
+
+static int usb_charger_get_property(struct power_supply *psy,
+				    enum power_supply_property psp,
+				    union power_supply_propval *val)
+{
+	struct usb_conn_info *info = power_supply_get_drvdata(psy);
+
+	switch (psp) {
+	case POWER_SUPPLY_PROP_ONLINE:
+		val->intval = info->last_role == USB_ROLE_DEVICE;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int usb_conn_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
+	struct power_supply_desc *desc;
 	struct usb_conn_info *info;
+	struct power_supply_config cfg = {
+		.of_node = dev->of_node,
+	};
 	int ret = 0;
 
 	info = devm_kzalloc(dev, sizeof(*info), GFP_KERNEL);
@@ -203,6 +234,20 @@ static int usb_conn_probe(struct platform_device *pdev)
 		}
 	}
 
+	desc = &info->desc;
+	desc->name = "usb-charger";
+	desc->properties = usb_charger_properties;
+	desc->num_properties = ARRAY_SIZE(usb_charger_properties);
+	desc->get_property = usb_charger_get_property;
+	desc->type = POWER_SUPPLY_TYPE_USB;
+	cfg.drv_data = info;
+
+	info->charger = devm_power_supply_register(dev, desc, &cfg);
+	if (IS_ERR(info->charger)) {
+		dev_err(dev, "Unable to register charger\n");
+		return PTR_ERR(info->charger);
+	}
+
 	platform_set_drvdata(pdev, info);
 
 	/* Perform initial detection */