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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Fri, 21 Jul 2023 09:32:58 +0300
Message-ID: <CAHp75Vf6FTgHyimX+B80tZEwJRg7ut1=DS=Dbdy+Aa+xVwh5YQ@mail.gmail.com>
Subject: Re: [PATCH] backlight: gpio_backlight: Drop output gpio direction
 check for initial power state
To:     Ying Liu <victor.liu@nxp.com>
Cc:     Daniel Thompson <daniel.thompson@linaro.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "linux-fbdev@vger.kernel.org" <linux-fbdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "lee@kernel.org" <lee@kernel.org>,
        "jingoohan1@gmail.com" <jingoohan1@gmail.com>,
        "deller@gmx.de" <deller@gmx.de>,
        Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <brgl@bgdev.pl>,
        Andy Shevchenko <andy@kernel.org>
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On Fri, Jul 21, 2023 at 8:17=E2=80=AFAM Ying Liu <victor.liu@nxp.com> wrote=
:
> On Thursday, July 20, 2023 7:28 PM Daniel Thompson <daniel.thompson@linar=
o.org> wrote:
> > On Thu, Jul 20, 2023 at 06:06:27AM +0000, Ying Liu wrote:
> > > Bootloader may leave gpio direction as input and gpio value as logica=
l low.
> > > It hints that initial backlight power state should be
> > FB_BLANK_POWERDOWN
> > > since the gpio value is literally logical low.
> >
> > To be honest this probably "hints" that the bootloader simply didn't
> > consider the backlight at all :-) . I'd rather the patch description
> > focus on what circumstances lead to the current code making a bad
> > decision. More like:
> >
> >   If the GPIO pin is in the input state but the backlight is currently
> >   off due to default pull downs then ...
>
> How about this patch description?
>
> ---------------------------------8<--------------------------------------=
-----
> Without this patch, if gpio pin is in input state but backlight is curren=
tly

s/Without this patch, if/If/

> 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:
> ---
> If in DT boot we have phandle link then leave the GPIO in a state which t=
he
> bootloader left it and let the user of the backlight to configure it furt=
her.
> ---
>
> So, let's drop output gpio direction check and only check gpio value to s=
et
> the initial power state.
> ---------------------------------8<--------------------------------------=
-----

--=20
With Best Regards,
Andy Shevchenko