[PATCH 4.14 39/74] gpiolib: fix up emulated open drain outputs

Greg Kroah-Hartman
2020-01-07T21:10:02Z

From: Russell King <rmk+kernel@armlinux.org.uk>

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>

---
drivers/gpio/gpiolib.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -206,6 +206,14 @@ int gpiod_get_direction(struct gpio_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 status;