linux-kernel - [PATCH] Input: elants_i2c: Properly handle the reset GPIO when power is off

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Date:   Thu, 17 Nov 2022 12:38:23 -0800
From:   Douglas Anderson <dianders@...omium.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Douglas Anderson <dianders@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        Johnny Chuang <johnny.chuang.emc@...il.com>,
        Scott Liu <scott.liu@....com.tw>, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] Input: elants_i2c: Properly handle the reset GPIO when power is off

As can be seen in elants_i2c_power_off(), we want the reset GPIO
asserted when power is off. The reset GPIO is active low so we need
the reset line logic low when power is off to avoid leakage.

We have a problem, though, at probe time. At probe time we haven't
powered the regulators on yet but we have:
  devm_gpiod_get(&client->dev, "reset", GPIOD_OUT_LOW);

While that _looks_ right, it turns out that it's not. The
GPIOD_OUT_LOW doesn't mean to init the GPIO to low. It means init the
GPIO to "not asserted". Since this is an active low GPIO that inits it
to be high.

Let's fix this to properly init the GPIO. Now after both probe and
power off the state of the GPIO is consistent (it's "asserted" or
level low).

Once we fix this, we can see that at power on time we no longer to
assert the reset GPIO as the first thing. The reset GPIO is _always_
asserted before powering on. Let's fix powering on to account for
this.

Fixes: afe10358e47a ("Input: elants_i2c - wire up regulator support")
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---
This issue was found mostly due to code inspection. A partner was
having issues with power sequencing with this touch screen and I
noticed this issue in the code. Though this patch doesn't seem to
fully address the problems that the partner was having (they are still
debugging), in the very least it seems correct and we should probably
take it.

This problem has been around for a while. Presumably the touchscreen
is tolerant enough to this short period of time at bootup where the
reset line was leaking power into the unpowered touchscreen, though
it's still not great.

 drivers/input/touchscreen/elants_i2c.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/input/touchscreen/elants_i2c.c b/drivers/input/touchscreen/elants_i2c.c
index 879a4d984c90..e1308e179dd6 100644
--- a/drivers/input/touchscreen/elants_i2c.c
+++ b/drivers/input/touchscreen/elants_i2c.c
@@ -1329,14 +1329,12 @@ static int elants_i2c_power_on(struct elants_data *ts)
 	if (IS_ERR_OR_NULL(ts->reset_gpio))
 		return 0;

-	gpiod_set_value_cansleep(ts->reset_gpio, 1);
-
 	error = regulator_enable(ts->vcc33);
 	if (error) {
 		dev_err(&ts->client->dev,
 			"failed to enable vcc33 regulator: %d\n",
 			error);
-		goto release_reset_gpio;
+		return error;
 	}

 	error = regulator_enable(ts->vccio);
@@ -1345,7 +1343,7 @@ static int elants_i2c_power_on(struct elants_data *ts)
 			"failed to enable vccio regulator: %d\n",
 			error);
 		regulator_disable(ts->vcc33);
-		goto release_reset_gpio;
+		return error;
 	}

 	/*
@@ -1354,7 +1352,6 @@ static int elants_i2c_power_on(struct elants_data *ts)
 	 */
 	udelay(ELAN_POWERON_DELAY_USEC);

-release_reset_gpio:
 	gpiod_set_value_cansleep(ts->reset_gpio, 0);
 	if (error)
 		return error;
@@ -1462,7 +1459,7 @@ static int elants_i2c_probe(struct i2c_client *client)
 		return error;
 	}

-	ts->reset_gpio = devm_gpiod_get(&client->dev, "reset", GPIOD_OUT_LOW);
+	ts->reset_gpio = devm_gpiod_get(&client->dev, "reset", GPIOD_OUT_HIGH);
 	if (IS_ERR(ts->reset_gpio)) {
 		error = PTR_ERR(ts->reset_gpio);

-- 
2.38.1.584.g0f3c55d4c2-goog