[PATCH v5.3, v4.19] gpiolib: don't clear FLAG_IS_OUT when emulating open-drain/open-source

[PATCH v5.3, v4.19] gpiolib: don't clear FLAG_IS_OUT when emulating open-drain/open-source

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.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@vger.kernel.org
Reported-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
[Bartosz: backported to v5.3, v4.19]
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.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 e4203c1eb869..74a77001b1bd 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -2775,8 +2775,10 @@ 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),
@@ -2784,8 +2786,10 @@ 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);
@@ -2793,6 +2797,17 @@ 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);
 
@@ -3153,8 +3168,6 @@ 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)
@@ -3184,8 +3197,6 @@ 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)
-- 
2.23.0

Re: [PATCH v5.3, v4.19] gpiolib: don't clear FLAG_IS_OUT when emulating open-drain/open-source

[Sasha Levin]

On Mon, Oct 14, 2019 at 05:54:35PM +0200, Bartosz Golaszewski wrote:
>From: Bartosz Golaszewski <bgolaszewski@baylibre.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@vger.kernel.org
>Reported-by: Kent Gibson <warthog618@gmail.com>
>Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
>[Bartosz: backported to v5.3, v4.19]
>Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

I've queued this and the 4.14 patch, thanks!

-- 
Thanks,
Sasha