linux-kernel - Re: [PATCH] leds: rt8515: add V4L2_FLASH_LED

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Date:   Mon, 15 Feb 2021 10:49:00 +0100
From:   Pavel Machek <pavel@....cz>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>, Dan Murphy <dmurphy@...com>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] leds: rt8515: add V4L2_FLASH_LED_CLASS dependency

Hi!

> > From: Arnd Bergmann <arnd@...db.de>
> >
> > The leds-rt8515 driver can optionall use the v4l2 flash led class,
> > but it causes a link error when that class is in a loadable module
> > and the rt8515 driver itself is built-in:
> >
> > ld.lld: error: undefined symbol: v4l2_flash_init
> > >>> referenced by leds-rt8515.c
> > >>>               leds/flash/leds-rt8515.o:(rt8515_probe) in archive
> > drivers/built-in.a
> >
> > Adding 'depends on V4L2_FLASH_LED_CLASS' in Kconfig would avoid that,
> > but it would make it impossible to use the driver without the
> > v4l2 support.
> >
> > Add the same dependency that the other users of this class have
> > instead, which just prevents the broken configuration.
> >
> > Fixes: e1c6edcbea13 ("leds: rt8515: Add Richtek RT8515 LED driver")
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> 
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> 
> > +       depends on V4L2_FLASH_LED_CLASS || !V4L2_FLASH_LED_CLASS
> 
> This kind of thing that looks like a truism but isn't is one of the
> most unintuitive
> things about KConfig :/ no idea what to do about it though.

This is the way it is usually fixed. Anyway, I applied it and pushed
it to Linus and it is now merged.

> I remember making a program for the C64 in early 1990ies with joke input
> such as y/n/m (yes/no/maybe), sadly in Kconfig this is no joke.

:-).

Best regards,
									Pavel
-- 
http://www.livejournal.com/~pavelmachek

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