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

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Message-ID: <CACRpkda+kWcaeF1WMetDp3ppbrbQmuFEiUbpTdq2kH7o7wN68Q@mail.gmail.com>
Date:   Mon, 24 Jul 2023 19:46:10 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
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>,
        "brgl@...ev.pl" <brgl@...ev.pl>
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,

Oh what an interesting corner case!

> 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>

The solutions seems fine.
Acked-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij