[PATCH] gpiolib: never report open-drain/source lines as 'input' to user-space

[PATCH] gpiolib: never report open-drain/source lines as 'input' to user-space

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

If the driver doesn't support open-drain/source config options, we
emulate this behavior when setting the direction by calling
gpiod_direction_input() if the default value is 0 (open-source) or
1 (open-drain), thus not actively driving the line in those cases.

This however clears the FLAG_IS_OUT bit for the GPIO line descriptor
and makes the LINEINFO ioctl() incorrectly report this line's mode as
'input' to user-space.

This commit modifies the ioctl() to always set the GPIOLINE_FLAG_IS_OUT
bit in the lineinfo structure's flags field. Since it's impossible to
use the input mode and open-drain/source options at the same time, we
can be sure the reported information will be correct.

Fixes: 521a2ad6f862 ("gpio: add userspace ABI for GPIO line information")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
---
 drivers/gpio/gpiolib.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index f497003f119c..80a2a2cb673b 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1091,9 +1091,11 @@ static long gpio_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		if (test_bit(FLAG_ACTIVE_LOW, &desc->flags))
 			lineinfo.flags |= GPIOLINE_FLAG_ACTIVE_LOW;
 		if (test_bit(FLAG_OPEN_DRAIN, &desc->flags))
-			lineinfo.flags |= GPIOLINE_FLAG_OPEN_DRAIN;
+			lineinfo.flags |= (GPIOLINE_FLAG_OPEN_DRAIN |
+					   GPIOLINE_FLAG_IS_OUT);
 		if (test_bit(FLAG_OPEN_SOURCE, &desc->flags))
-			lineinfo.flags |= GPIOLINE_FLAG_OPEN_SOURCE;
+			lineinfo.flags |= (GPIOLINE_FLAG_OPEN_SOURCE |
+					   GPIOLINE_FLAG_IS_OUT);
 
 		if (copy_to_user(ip, &lineinfo, sizeof(lineinfo)))
 			return -EFAULT;
-- 
2.21.0

Re: [PATCH] gpiolib: never report open-drain/source lines as 'input' to user-space

[Linus Walleij]

On Tue, Aug 6, 2019 at 1:41 PM Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
>
> If the driver doesn't support open-drain/source config options, we
> emulate this behavior when setting the direction by calling
> gpiod_direction_input() if the default value is 0 (open-source) or
> 1 (open-drain), thus not actively driving the line in those cases.
>
> This however clears the FLAG_IS_OUT bit for the GPIO line descriptor
> and makes the LINEINFO ioctl() incorrectly report this line's mode as
> 'input' to user-space.
>
> This commit modifies the ioctl() to always set the GPIOLINE_FLAG_IS_OUT
> bit in the lineinfo structure's flags field. Since it's impossible to
> use the input mode and open-drain/source options at the same time, we
> can be sure the reported information will be correct.
>
> Fixes: 521a2ad6f862 ("gpio: add userspace ABI for GPIO line information")
> Cc: stable <stable@vger.kernel.org>
> Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Patch applied for fixes!
Good catch.

Yours,
Linus Walleij