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

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Message-ID: <20240212124428.GB4593@aspen.lan>
Date: Mon, 12 Feb 2024 12:44:28 +0000
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Lee Jones <lee@...nel.org>, Jingoo Han <jingoohan1@...il.com>,
	Helge Deller <deller@....de>,
	Duje Mihanović <duje.mihanovic@...le.hr>,
	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 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:
~~~
diff --git a/drivers/leds/Kconfig b/drivers/leds/Kconfig
index 64bb2de237e95..a08816cde78ae 100644
--- a/drivers/leds/Kconfig
+++ b/drivers/leds/Kconfig
@@ -186,10 +186,6 @@ config LEDS_EL15203000
          To compile this driver as a module, choose M here: the module
          will be called leds-el15203000.

-config LEDS_EXPRESSWIRE
-       bool
-       depends on GPIOLIB
-
 config LEDS_TURRIS_OMNIA
        tristate "LED support for CZ.NIC's Turris Omnia"
        depends on LEDS_CLASS_MULTICOLOR
@@ -936,3 +932,10 @@ comment "Simple LED drivers"
 source "drivers/leds/simple/Kconfig"

 endif # NEW_LEDS
+
+# This is library code that is useful for LEDs but can be enable/disabled
+# independently of NEW_LEDS. In fact it must be independent so it can be
+# selected from other sub-systems.
+config LEDS_EXPRESSWIRE
+       bool
+       depends on GPIOLIB
~~~

Alternatively we could add a "depends on NEW_LEDS" alongside the
existing select or just make LEDS_EXPRESSWIRE user selectable.

It also looks like we should put back the GPIOLIB dependency to both
 KTD2801 and KTD2692... and I'll take a mea-culpa for providing bad
 advice during the review cycles!


Daniel.