Re: [PATCH] gpiolib: fix up emulated open drain outputs

[Kent Gibson <warthog618@xxxxxxxxx>]

On Sat, Dec 07, 2019 at 04:20:18PM +0000, Russell King wrote:
> 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@xxxxxxxxxx>
> Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
> ---
>  drivers/gpio/gpiolib.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 32c2048deb8c..70c60aac41cc 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -220,6 +220,14 @@ int gpiod_get_direction(struct gpio_desc *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;
> +

What about the FLAG_OPEN_SOURCE case?

Kent.

>  	if (!chip->get_direction)
>  		return -ENOTSUPP;
>  
> -- 
> 2.20.1
>