linux-kernel - Re: [PATCH] gpiolib: Show correct direction from the beginning

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Date:   Wed, 19 Sep 2018 06:04:17 +0200
From:   Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Timur Tabi <timur@...eaurora.org>, swboyd@...omium.org,
        linux-gpio@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: Show correct direction from the beginning

Hi Linus
On Wed, Sep 19, 2018 at 12:40 AM Linus Walleij <linus.walleij@...aro.org> wrote:
>
> On Fri, Sep 14, 2018 at 12:08 AM Ricardo Ribalda Delgado
> <ricardo.ribalda@...il.com> wrote:
>
> > Current code assumes that the direction is input if direction_input
> > function is set.
> > This might not be the case on GPIOs with programmable direction.
> >
> > Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
> > ---
> >  drivers/gpio/gpiolib.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index a57300c1d649..af853749e0bb 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -1352,7 +1352,12 @@ int gpiochip_add_data_with_key(struct gpio_chip *chip, void *data,
> >                  * it does, and in case chip->get_direction is not set, we may
> >                  * expose the wrong direction in sysfs.
> >                  */
> > -               desc->flags = !chip->direction_input ? (1 << FLAG_IS_OUT) : 0;
> > +               if (chip->get_direction)
> > +                       desc->flags = !chip->get_direction(chip, i) ?
> > +                                       (1 << FLAG_IS_OUT) : 0;
> > +               else
> > +                       desc->flags = !chip->direction_input ?
> > +                                       (1 << FLAG_IS_OUT) : 0;
>
> We used to do this.
>
> But it breaks Qualcomm hardware.

And should't that be tacked in qcom hardware with something like:

if (!priv->initialized)
   return INPUT;

if you or Timur point me to the harware that was crashing I would not
mind looking into that, but the current situations seems to me like a
hack.

Other option would be to implement a new function get_direction_fast()
(the name could be better). I can also try to implement something in
that direction if you want.

Thanks for your review.

>
> commit 1ca2a92b2a99323f666f1b669b7484df4bda05e4
> Author: Timur Tabi <timur@...eaurora.org>
> Date:   Wed Dec 20 13:10:31 2017 -0600
>
>     Revert "gpio: set up initial state from .get_direction()"
>
>     This reverts commit 72d3200061776264941be1b5a9bb8e926b3b30a5.
>
>     We cannot blindly query the direction of all GPIOs when the pins are
>     first registered.  The get_direction callback normally triggers a
>     read/write to hardware, but we shouldn't be touching the hardware for
>     an individual GPIO until after it's been properly claimed.
>
>     Signed-off-by: Timur Tabi <timur@...eaurora.org>
>     Reviewed-by: Stephen Boyd <sboyd@...eaurora.org>
>     Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
>
> Yours,
> Linus Walleij



-- 
Ricardo Ribalda