linux-kernel - Re: [PATCH v2] gpiolib: Preserve desc->flags when setting state

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Message-ID: <CACRpkdbWWWhQ5V5tc0FkQSx80ZXZ+ki-mn9Cc_Vm-jOwVu0R3A@mail.gmail.com>
Date:   Fri, 5 Jul 2019 23:55:51 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Chris Packham <chris.packham@...iedtelesis.co.nz>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] gpiolib: Preserve desc->flags when setting state

Hi Chris,

thanks for your patch!

On Thu, Jul 4, 2019 at 6:21 AM Chris Packham
<chris.packham@...iedtelesis.co.nz> wrote:

> desc->flags may already have values set by of_gpiochip_add() so make
> sure that this isn't undone when setting the initial direction.
>
> Fixes: 3edfb7bd76bd1cba ("gpiolib: Show correct direction from the beginning")
> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
> ---
>
> Notes:
>     Changes in v2:
>     - add braces to avoid ambiguious else warning

This is almost the solution!

> -               if (chip->get_direction && gpiochip_line_is_valid(chip, i))
> -                       desc->flags = !chip->get_direction(chip, i) ?
> -                                       (1 << FLAG_IS_OUT) : 0;
> -               else
> -                       desc->flags = !chip->direction_input ?
> -                                       (1 << FLAG_IS_OUT) : 0;
> +               if (chip->get_direction && gpiochip_line_is_valid(chip, i)) {
> +                       if (!chip->get_direction(chip, i))
> +                               set_bit(FLAG_IS_OUT, &desc->flags);

You need to clear_bit() in the reverse case. We just learned we can't
assume anything about the flags here, like just assign them.

> +               } else {
> +                       if (!chip->direction_input)
> +                               set_bit(FLAG_IS_OUT, &desc->flags);

Same here.

Yours,
Linus Walleij