linux-kernel - [PATCH] gpiolib: don't allow OPEN_DRAIN & OPEN

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Date:   Wed, 15 Nov 2017 16:47:43 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <brgl@...ev.pl>
Subject: [PATCH] gpiolib: don't allow OPEN_DRAIN & OPEN_SOURCE flags simultaneously

Do not allow OPEN_SOURCE & OPEN_DRAIN flags in a single request. If
the hardware actually supports enabling both at the same time the
electrical result would be disastrous.

Suggested-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Bartosz Golaszewski <brgl@...ev.pl>
---
There was a misunderstanding as to what the goal of my previous commit
609aaf6a6029 ("gpiolib: don't allow OPEN_DRAIN & OPEN_SOURCE flags for
input") was, which resulted in discovering another thing that needs
fixing. This change was suggested to me by Linus earlier today.

 drivers/gpio/gpiolib.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 641a5eb552cb..ec80e0146fd5 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -459,6 +459,15 @@ static int linehandle_create(struct gpio_device *gdev, void __user *ip)
 	if (lflags & ~GPIOHANDLE_REQUEST_VALID_FLAGS)
 		return -EINVAL;
 
+	/*
+	 * Do not allow OPEN_SOURCE & OPEN_DRAIN flags in a single request. If
+	 * the hardware actually supports enabling both at the same time the
+	 * electrical result would be disastrous.
+	 */
+	if ((lflags & GPIOHANDLE_REQUEST_OPEN_DRAIN) &&
+	    (lflags & GPIOHANDLE_REQUEST_OPEN_SOURCE))
+		return -EINVAL;
+
 	/* OPEN_DRAIN and OPEN_SOURCE flags only make sense for output mode. */
 	if (!(lflags & GPIOHANDLE_REQUEST_OUTPUT) &&
 	    ((lflags & GPIOHANDLE_REQUEST_OPEN_DRAIN) ||
-- 
2.13.2