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

[Russell King - ARM Linux admin <linux@xxxxxxxxxxxxxxx>]

On Sun, Dec 08, 2019 at 11:43:40AM +0800, Kent Gibson wrote:
> 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?

do you have a scenario you can test?

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