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

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Message-ID: <lsq.1587683028.908662902@decadent.org.uk>
Date:   Fri, 24 Apr 2020 00:05:19 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Bartosz Golaszewski" <bgolaszewski@...libre.com>,
        "Linus Walleij" <linus.walleij@...aro.org>,
        "Russell King" <rmk+kernel@...linux.org.uk>
Subject: [PATCH 3.16 092/245] gpiolib: fix up emulated open drain outputs

3.16.83-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Russell King <rmk+kernel@...linux.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@...aro.org>
Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
Signed-off-by: Ben Hutchings <ben@...adent.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;