[PATCH 4/6] HID: i2c-hid: elan: fix reset suspend current leakage

[Johan Hovold <johan+linaro@kernel.org>]

The Elan eKTH5015M touch controller found on the Lenovo ThinkPad X13s
shares the VCC33 supply with other peripherals that may remain powered
during suspend (e.g. when enabled as wakeup sources).

The reset line is also wired so that it can be left deasserted when the
supply is off.

This is important as it avoids holding the controller in reset for
extended periods of time when it remains powered, which can lead to
increased power consumption, and also avoids leaking current through the
X13s reset circuitry during suspend (and after driver unbind).

Use the new 'no-reset-on-power-off' devicetree property to determine
when reset needs to be asserted on power down.

Notably this also avoids wasting power on machine variants without a
touchscreen for which the driver would otherwise exit probe with reset
asserted.

Fixes: bd3cba00dcc6 ("HID: i2c-hid: elan: Add support for Elan eKTH6915 i2c-hid touchscreens")
Cc: stable@vger.kernel.org	# 6.0
Cc: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---
 drivers/hid/i2c-hid/i2c-hid-of-elan.c | 37 ++++++++++++++++++++-------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/drivers/hid/i2c-hid/i2c-hid-of-elan.c b/drivers/hid/i2c-hid/i2c-hid-of-elan.c
index 5b91fb106cfc..8a905027d5e9 100644
--- a/drivers/hid/i2c-hid/i2c-hid-of-elan.c
+++ b/drivers/hid/i2c-hid/i2c-hid-of-elan.c
@@ -31,6 +31,7 @@ struct i2c_hid_of_elan {
 	struct regulator *vcc33;
 	struct regulator *vccio;
 	struct gpio_desc *reset_gpio;
+	bool no_reset_on_power_off;
 	const struct elan_i2c_hid_chip_data *chip_data;
 };
 
@@ -40,17 +41,17 @@ static int elan_i2c_hid_power_up(struct i2chid_ops *ops)
 		container_of(ops, struct i2c_hid_of_elan, ops);
 	int ret;
 
+	gpiod_set_value_cansleep(ihid_elan->reset_gpio, 1);
+
 	if (ihid_elan->vcc33) {
 		ret = regulator_enable(ihid_elan->vcc33);
 		if (ret)
-			return ret;
+			goto err_deassert_reset;
 	}
 
 	ret = regulator_enable(ihid_elan->vccio);
-	if (ret) {
-		regulator_disable(ihid_elan->vcc33);
-		return ret;
-	}
+	if (ret)
+		goto err_disable_vcc33;
 
 	if (ihid_elan->chip_data->post_power_delay_ms)
 		msleep(ihid_elan->chip_data->post_power_delay_ms);
@@ -60,6 +61,15 @@ static int elan_i2c_hid_power_up(struct i2chid_ops *ops)
 		msleep(ihid_elan->chip_data->post_gpio_reset_on_delay_ms);
 
 	return 0;
+
+err_disable_vcc33:
+	if (ihid_elan->vcc33)
+		regulator_disable(ihid_elan->vcc33);
+err_deassert_reset:
+	if (ihid_elan->no_reset_on_power_off)
+		gpiod_set_value_cansleep(ihid_elan->reset_gpio, 0);
+
+	return ret;
 }
 
 static void elan_i2c_hid_power_down(struct i2chid_ops *ops)
@@ -67,7 +77,14 @@ static void elan_i2c_hid_power_down(struct i2chid_ops *ops)
 	struct i2c_hid_of_elan *ihid_elan =
 		container_of(ops, struct i2c_hid_of_elan, ops);
 
-	gpiod_set_value_cansleep(ihid_elan->reset_gpio, 1);
+	/*
+	 * Do not assert reset when the hardware allows for it to remain
+	 * deasserted regardless of the state of the (shared) power supply to
+	 * avoid wasting power when the supply is left on.
+	 */
+	if (!ihid_elan->no_reset_on_power_off)
+		gpiod_set_value_cansleep(ihid_elan->reset_gpio, 1);
+
 	if (ihid_elan->chip_data->post_gpio_reset_off_delay_ms)
 		msleep(ihid_elan->chip_data->post_gpio_reset_off_delay_ms);
 
@@ -87,12 +104,14 @@ static int i2c_hid_of_elan_probe(struct i2c_client *client)
 	ihid_elan->ops.power_up = elan_i2c_hid_power_up;
 	ihid_elan->ops.power_down = elan_i2c_hid_power_down;
 
-	/* Start out with reset asserted */
-	ihid_elan->reset_gpio =
-		devm_gpiod_get_optional(&client->dev, "reset", GPIOD_OUT_HIGH);
+	ihid_elan->reset_gpio = devm_gpiod_get_optional(&client->dev, "reset",
+							GPIOD_ASIS);
 	if (IS_ERR(ihid_elan->reset_gpio))
 		return PTR_ERR(ihid_elan->reset_gpio);
 
+	ihid_elan->no_reset_on_power_off = of_property_read_bool(client->dev.of_node,
+						"no-reset-on-power-off");
+
 	ihid_elan->vccio = devm_regulator_get(&client->dev, "vccio");
 	if (IS_ERR(ihid_elan->vccio))
 		return PTR_ERR(ihid_elan->vccio);
-- 
2.43.2