[PATCH 3.16 092/245] gpiolib: fix up emulated open drain outputs

Ben Hutchings
2020-04-23T23:17:51Z

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.

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: Ben Hutchings <ben@decadent.org.uk>
---
drivers/gpio/gpiolib.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -273,6 +273,14 @@ int gpiod_get_direction(const struct gpi
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;