linux-kernel - Re: [PATCH] backlight: ktd2801: fix LED dependency

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Message-ID: <20240213170720.GA297704@aspen.lan>
Date: Tue, 13 Feb 2024 17:07:20 +0000
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Duje Mihanović <duje.mihanovic@...le.hr>
Cc: Arnd Bergmann <arnd@...nel.org>, Lee Jones <lee@...nel.org>,
	Jingoo Han <jingoohan1@...il.com>, Helge Deller <deller@....de>,
	Linus Walleij <linus.walleij@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, Flavio Suligoi <f.suligoi@...m.it>,
	Hans de Goede <hdegoede@...hat.com>,
	Jianhua Lu <lujianhua000@...il.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] backlight: ktd2801: fix LED dependency

On Mon, Feb 12, 2024 at 03:31:50PM +0100, Duje Mihanović wrote:
> On Monday, February 12, 2024 1:44:28 PM CET Daniel Thompson wrote:
> > On Mon, Feb 12, 2024 at 12:18:12PM +0100, Arnd Bergmann wrote:
> > > From: Arnd Bergmann <arnd@...db.de>
> > >
> > > The new backlight driver unconditionally selects LEDS_EXPRESSWIRE, which
> > > is in a different subsystem that may be disabled here:
> > >
> > > WARNING: unmet direct dependencies detected for LEDS_EXPRESSWIRE
> > >
> > >   Depends on [n]: NEW_LEDS [=n] && GPIOLIB [=y]
> > >   Selected by [y]:
> > >   - BACKLIGHT_KTD2801 [=y] && HAS_IOMEM [=y] && BACKLIGHT_CLASS_DEVICE
> [=y]
> > >
> > > Change the select to depends, to ensure the indirect dependency is
> > > met as well even when LED support is disabled.
> > >
> > > Fixes: 66c76c1cd984 ("backlight: Add Kinetic KTD2801 backlight support")
> > > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > > ---
> > >
> > >  drivers/video/backlight/Kconfig | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/video/backlight/Kconfig
> > > b/drivers/video/backlight/Kconfig index 230bca07b09d..f83f9ef037fc 100644
> > > --- a/drivers/video/backlight/Kconfig
> > > +++ b/drivers/video/backlight/Kconfig
> > > @@ -185,7 +185,7 @@ config BACKLIGHT_KTD253
> > >
> > >  config BACKLIGHT_KTD2801
> > >
> > >  	tristate "Backlight Driver for Kinetic KTD2801"
> > >
> > > -	select LEDS_EXPRESSWIRE
> > > +	depends on LEDS_EXPRESSWIRE
> >
> > As far as I can tell this resolves the warning by making it impossible
> > to enable BACKLIGHT_KTD2801 unless a largely unrelated driver
> > (LEDS_KTD2692) is also enabled!
> >
> > A better way to resolve this problem might be to eliminate the NEW_LEDS
> > dependency entirely:
>
> I believe this would be the best thing to do here. Making LEDS_EXPRESSWIRE
> user selectable doesn't make much sense to me as the library is rather low-
> level (a quick grep turns up BTREE as an example of something similar) and IMO
> the GPIOLIB dependency should be handled by LEDS_EXPRESSWIRE as it's the one
> actually using the GPIO interface (except maybe for KTD2692 as it has some
> extra GPIOs not present in the other one and thus handles them itself).

We can keep the GPIOLIB dependency in LEDS_EXPRESSWIRE but it also needs
to be included in the KTD2801 KConfig too... otherwise we'll get similar
problems to the ones Arnd addressed here:
https://lore.kernel.org/all/20240213165602.2230970-1-arnd@kernel.org/


Daniel.