[PATCH 7/7] power: supply: axp20x_usb_power: Only poll while offline

[Samuel Holland <samuel@sholland.org>]

Investigation on the AXP803 shows that VBUS_PLUGIN/VBUS_REMOVAL IRQs are
triggered on the rising/falling edge of AXP20X_PWR_STATUS_VBUS_USED. The
reason IRQs do not arrive while N_VBUSEN/DRIVEVBUS is high is because
AXP20X_PWR_STATUS_VBUS_USED also never goes high.

This also means that if VBUS is online, a VBUS_REMOVAL IRQ is received
immediately on setting N_VBUSEN/DRIVEVBUS high (and VBUS_PLUGIN shortly
after it is set back low). This was also verified to be the case when
manually offlining VBUS through AXP20X_VBUS_PATH_SELECT.

Therefore, as long as VBUS is online, a present->absent transition
necessarily implies an online->offline transition. This will cause an
IRQ, and so there is no need to poll.

Signed-off-by: Samuel Holland <samuel@sholland.org>
---
 drivers/power/supply/axp20x_usb_power.c | 35 ++++++++++++++++++-------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/drivers/power/supply/axp20x_usb_power.c b/drivers/power/supply/axp20x_usb_power.c
index 16062b2c7ea8..0993ea03f303 100644
--- a/drivers/power/supply/axp20x_usb_power.c
+++ b/drivers/power/supply/axp20x_usb_power.c
@@ -67,16 +67,39 @@ struct axp20x_usb_power {
 	struct iio_channel *vbus_i;
 	struct delayed_work vbus_detect;
 	unsigned int old_status;
+	bool online;
 	unsigned int num_irqs;
 	unsigned int irqs[];
 };
 
+static bool axp20x_usb_vbus_needs_polling(struct axp20x_usb_power *power)
+{
+	/*
+	 * Polling is only necessary while VBUS is offline. While online, a
+	 * present->absent transition implies an online->offline transition
+	 * and will triger the VBUS_REMOVAL IRQ.
+	 */
+	if (power->axp20x_id >= AXP221_ID && !power->online)
+		return true;
+
+	return false;
+}
+
 static irqreturn_t axp20x_usb_power_irq(int irq, void *devid)
 {
 	struct axp20x_usb_power *power = devid;
 
+	/*
+	 * VBUS_PLUGIN/VBUS_REMOVAL are triggered on transitions of
+	 * AXP20X_PWR_STATUS_VBUS_USED.
+	 */
+	power->online = irq == power->irqs[0];
+
 	power_supply_changed(power->supply);
 
+	if (axp20x_usb_vbus_needs_polling(power))
+		mod_delayed_work(system_wq, &power->vbus_detect, DEBOUNCE_TIME);
+
 	return IRQ_HANDLED;
 }
 
@@ -96,17 +119,11 @@ static void axp20x_usb_power_poll_vbus(struct work_struct *work)
 		power_supply_changed(power->supply);
 
 	power->old_status = val;
+	power->online = val & AXP20X_PWR_STATUS_VBUS_USED;
 
 out:
-	mod_delayed_work(system_wq, &power->vbus_detect, DEBOUNCE_TIME);
-}
-
-static bool axp20x_usb_vbus_needs_polling(struct axp20x_usb_power *power)
-{
-	if (power->axp20x_id >= AXP221_ID)
-		return true;
-
-	return false;
+	if (axp20x_usb_vbus_needs_polling(power))
+		mod_delayed_work(system_wq, &power->vbus_detect, DEBOUNCE_TIME);
 }
 
 static int axp20x_get_current_max(struct axp20x_usb_power *power, int *val)
-- 
2.23.0