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

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Date:   Tue, 18 Sep 2018 15:40:10 -0700
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
        Timur Tabi <timur@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: Show correct direction from the beginning

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.

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