sunxi: axp221: Add support for controlling the drivebus pin

The axp221 / axp223's N_VBUSEN pin can be configured as an output rather
then an input, add axp_drivebus_enable() and _disable() functions to set
the pin in output mode and control it.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
diff --git a/drivers/power/axp221.c b/drivers/power/axp221.c
index 728727b..4c86f09 100644
--- a/drivers/power/axp221.c
+++ b/drivers/power/axp221.c
@@ -353,3 +353,39 @@
 
 	return 0;
 }
+
+static int axp_drivebus_setup(void)
+{
+	int ret;
+
+	ret = axp221_init();
+	if (ret)
+		return ret;
+
+	/* Set N_VBUSEN pin to output / DRIVEBUS function */
+	return axp221_clrbits(AXP221_MISC_CTRL, AXP221_MISC_CTRL_N_VBUSEN_FUNC);
+}
+
+int axp_drivebus_enable(void)
+{
+	int ret;
+
+	ret = axp_drivebus_setup();
+	if (ret)
+		return ret;
+
+	/* Set DRIVEBUS high */
+	return axp221_setbits(AXP221_VBUS_IPSOUT, AXP221_VBUS_IPSOUT_DRIVEBUS);
+}
+
+int axp_drivebus_disable(void)
+{
+	int ret;
+
+	ret = axp_drivebus_setup();
+	if (ret)
+		return ret;
+
+	/* Set DRIVEBUS low */
+	return axp221_clrbits(AXP221_VBUS_IPSOUT, AXP221_VBUS_IPSOUT_DRIVEBUS);
+}