linux-kernel - Re: [PATCH v4] backlight: gpio_backlight: Drop output GPIO direction check for initial power state

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Message-ID: <CAMRc=MfPKQuEGrFXuPNOKchE_Fj+obOheDoemoF9rxtRWYiFCg@mail.gmail.com>
Date:   Fri, 21 Jul 2023 13:07:34 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Ying Liu <victor.liu@....com>
Cc:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "lee@...nel.org" <lee@...nel.org>,
        "daniel.thompson@...aro.org" <daniel.thompson@...aro.org>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "deller@....de" <deller@....de>,
        "andy@...nel.org" <andy@...nel.org>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>
Subject: Re: [PATCH v4] backlight: gpio_backlight: Drop output GPIO direction
 check for initial power state

On Fri, Jul 21, 2023 at 11:29 AM Ying Liu <victor.liu@....com> wrote:
>
> If GPIO pin is in input state but backlight is currently off due to
> default pull downs, then initial power state is set to FB_BLANK_UNBLANK
> in DT boot mode with phandle link and the backlight is effectively
> turned on in gpio_backlight_probe(), which is undesirable according to
> patch description of commit ec665b756e6f ("backlight: gpio-backlight:
> Correct initial power state handling").
>
> Quote:
> ---8<---
> If in DT boot we have phandle link then leave the GPIO in a state which the
> bootloader left it and let the user of the backlight to configure it further.
> ---8<---
>
> So, let's drop output GPIO direction check and only check GPIO value to set
> the initial power state.
>
> Fixes: 706dc68102bc ("backlight: gpio: Explicitly set the direction of the GPIO")
> Signed-off-by: Liu Ying <victor.liu@....com>
> ---
> v3->v4:
> * Capitalize words 'gpio' in patch description. (Andy)
> * Capitalize word 'gpio' in patch title.
> * Quote appropriately in patch description. (Andy)
>
> v2->v3:
> * Add Fixes tag. (Daniel)
>
> v1->v2:
> * Improve patch description. (Daniel, Bartosz, Andy)
>
>  drivers/video/backlight/gpio_backlight.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/video/backlight/gpio_backlight.c b/drivers/video/backlight/gpio_backlight.c
> index 6f78d928f054..38c46936fdcd 100644
> --- a/drivers/video/backlight/gpio_backlight.c
> +++ b/drivers/video/backlight/gpio_backlight.c
> @@ -87,8 +87,7 @@ static int gpio_backlight_probe(struct platform_device *pdev)
>                 /* Not booted with device tree or no phandle link to the node */
>                 bl->props.power = def_value ? FB_BLANK_UNBLANK
>                                             : FB_BLANK_POWERDOWN;
> -       else if (gpiod_get_direction(gbl->gpiod) == 0 &&
> -                gpiod_get_value_cansleep(gbl->gpiod) == 0)
> +       else if (gpiod_get_value_cansleep(gbl->gpiod) == 0)
>                 bl->props.power = FB_BLANK_POWERDOWN;
>         else
>                 bl->props.power = FB_BLANK_UNBLANK;
> --
> 2.37.1
>

Acked-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>