From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Kent Gibson <warthog618@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>,
Bartosz Golaszewski <bgolaszewski@baylibre.com>,
linux-gpio@vger.kernel.org
Subject: Re: [PATCH] gpiolib: fix up emulated open drain outputs
Date: Sun, 8 Dec 2019 07:18:23 +0000 [thread overview]
Message-ID: <20191208071823.GZ25745@shell.armlinux.org.uk> (raw)
In-Reply-To: <20191208034340.GA9333@sol>
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@linaro.org>
> > Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
> > ---
> > 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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next prev parent reply other threads:[~2019-12-08 7:18 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-07 16:20 [PATCH] gpiolib: fix up emulated open drain outputs Russell King
2019-12-08 3:43 ` Kent Gibson
2019-12-08 7:18 ` Russell King - ARM Linux admin [this message]
2019-12-08 7:51 ` Kent Gibson
2019-12-08 13:02 ` Russell King - ARM Linux admin
2019-12-08 13:34 ` Kent Gibson
2019-12-11 9:39 ` Bartosz Golaszewski
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