linux-kernel - Re: drivers/leds/flash/leds-rt8515.c:216: undefined reference to `v4l2_flash

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Date:   Fri, 12 Feb 2021 13:38:58 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     kernel test robot <lkp@...el.com>, Arnd Bergmann <arnd@...db.de>
Cc:     kbuild-all@...ts.01.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Pavel Machek <pavel@....cz>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: drivers/leds/flash/leds-rt8515.c:216: undefined reference to `v4l2_flash_release'

I need Arnds help with this...

On Fri, Feb 12, 2021 at 12:05 AM kernel test robot <lkp@...el.com> wrote:

>    ld: drivers/leds/flash/leds-rt8515.o: in function `rt8515_v4l2_flash_release':
> >> drivers/leds/flash/leds-rt8515.c:216: undefined reference to `v4l2_flash_release'
>    ld: drivers/leds/flash/leds-rt8515.o: in function `rt8515_probe':
>    drivers/leds/flash/leds-rt8515.c:354: undefined reference to `v4l2_flash_init'

So the problem is that this is compiled in, so CONFIG_LEDS_RT8515=y
(it is tristate so can also be a module)
but it depends on symbols from a module:
CONFIG_V4L2_FLASH_LED_CLASS=m.

In the code I try to only support the V4L2 interface when using V4L2:
#if IS_ENABLED(CONFIG_V4L2_FLASH_LED_CLASS)
(... V4L2 code...)

Is there a way to define in Kconfig that if and only if you enable
this other module it has to follow the y or m that we use for this
driver?

Or do I simply have to bite the bullet, make it bool and
depend on CONFIG_V4L2_FLASH_LED_CLASS || !CONFIG_V4L2_FLASH_LED_CLASS
?

Yours,
Linus Walleij