linux-kernel - [PATCH] gpiolib: don't clear FLAG_IS_OUT when emulating open-drain/open-source

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Date:   Tue, 10 Sep 2019 10:21:38 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        stable@...r.kernel.org, Kent Gibson <warthog618@...il.com>
Subject: [PATCH] gpiolib: don't clear FLAG_IS_OUT when emulating open-drain/open-source

From: Bartosz Golaszewski <bgolaszewski@...libre.com>

When emulating open-drain/open-source by not actively driving the output
lines - we're simply changing their mode to input. This is wrong as it
will then make it impossible to change the value of such line - it's now
considered to actually be in input mode. If we want to still use the
direction_input() callback for simplicity then we need to set FLAG_IS_OUT
manually in gpiod_direction_output() and not clear it in
gpio_set_open_drain_value_commit() and
gpio_set_open_source_value_commit().

Fixes: c663e5f56737 ("gpio: support native single-ended hardware drivers")
Cc: stable@...r.kernel.org
Reported-by: Kent Gibson <warthog618@...il.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
---
 drivers/gpio/gpiolib.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index cca749010cd0..6bb4191d3844 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2769,8 +2769,10 @@ int gpiod_direction_output(struct gpio_desc *desc, int value)
 		if (!ret)
 			goto set_output_value;
 		/* Emulate open drain by not actively driving the line high */
-		if (value)
-			return gpiod_direction_input(desc);
+		if (value) {
+			ret = gpiod_direction_input(desc);
+			goto set_output_flag;
+		}
 	}
 	else if (test_bit(FLAG_OPEN_SOURCE, &desc->flags)) {
 		ret = gpio_set_config(gc, gpio_chip_hwgpio(desc),
@@ -2778,8 +2780,10 @@ int gpiod_direction_output(struct gpio_desc *desc, int value)
 		if (!ret)
 			goto set_output_value;
 		/* Emulate open source by not actively driving the line low */
-		if (!value)
-			return gpiod_direction_input(desc);
+		if (!value) {
+			ret = gpiod_direction_input(desc);
+			goto set_output_flag;
+		}
 	} else {
 		gpio_set_config(gc, gpio_chip_hwgpio(desc),
 				PIN_CONFIG_DRIVE_PUSH_PULL);
@@ -2787,6 +2791,17 @@ int gpiod_direction_output(struct gpio_desc *desc, int value)
 
 set_output_value:
 	return gpiod_direction_output_raw_commit(desc, value);
+
+set_output_flag:
+	/*
+	 * When emulating open-source or open-drain functionalities by not
+	 * actively driving the line (setting mode to input) we still need to
+	 * set the IS_OUT flag or otherwise we won't be able to set the line
+	 * value anymore.
+	 */
+	if (ret == 0)
+		set_bit(FLAG_IS_OUT, &desc->flags);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(gpiod_direction_output);
 
@@ -3147,8 +3162,6 @@ static void gpio_set_open_drain_value_commit(struct gpio_desc *desc, bool value)
 
 	if (value) {
 		err = chip->direction_input(chip, offset);
-		if (!err)
-			clear_bit(FLAG_IS_OUT, &desc->flags);
 	} else {
 		err = chip->direction_output(chip, offset, 0);
 		if (!err)
@@ -3178,8 +3191,6 @@ static void gpio_set_open_source_value_commit(struct gpio_desc *desc, bool value
 			set_bit(FLAG_IS_OUT, &desc->flags);
 	} else {
 		err = chip->direction_input(chip, offset);
-		if (!err)
-			clear_bit(FLAG_IS_OUT, &desc->flags);
 	}
 	trace_gpio_direction(desc_to_gpio(desc), !value, err);
 	if (err < 0)
-- 
2.21.0