gpiolib: fix up emulated open drain outputs

BugLink: https://bugs.launchpad.net/bugs/1861710
commit 256efaea1fdc4e38970489197409a26125ee0aaa upstream.

gpiolib has a corner case with open drain outputs that are emulated.
When such outputs are outputting a logic 1, emulation will set the
hardware to input mode, which will cause gpiod_get_direction() to
report that it is in input mode. This is different from the behaviour
with a true open-drain output.

Unify the semantics here.

Cc: <stable@vger.kernel.org>
Suggested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 74a77001b1bd73aa25ba6a18b399ebd7e9dceab6..84967bc7bf0a361ebc99d2ea91bde4acd4cfe3c4 100644 (file)
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -218,6 +218,14 @@ int gpiod_get_direction(struct gpio_desc *desc)
        chip = gpiod_to_chip(desc);
        offset = gpio_chip_hwgpio(desc);
 
+       /*
+        * Open drain emulation using input mode may incorrectly report
+        * input here, fix that up.
+        */
+       if (test_bit(FLAG_OPEN_DRAIN, &desc->flags) &&
+           test_bit(FLAG_IS_OUT, &desc->flags))
+               return 0;
+
        if (!chip->get_direction)
                return -ENOTSUPP;