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Date:   Tue, 19 Jul 2022 04:54:03 +0000
From:   Tzung-Bi Shih <tzungbi@kernel.org>
To:     Guenter Roeck <groeck@google.com>
Cc:     Benson Leung <bleung@chromium.org>,
        Guenter Roeck <groeck@chromium.org>,
        "open list:CHROME HARDWARE PLATFORM SUPPORT" 
        <chrome-platform@lists.linux.dev>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        kernel test robot <lkp@intel.com>
Subject: Re: [PATCH v2] platform/chrome: cros_kbd_led_backlight: fix build
 warning
Message-ID: <YtY460lI465ne00L@google.com>
References: <20220718105047.2356542-1-tzungbi@kernel.org>
 <CABXOdTdKpqsqajhQzQ1aEp6bsa96ONN6nz9EWZv6jGSuN0_LTA@mail.gmail.com>
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On Mon, Jul 18, 2022 at 06:28:22AM -0700, Guenter Roeck wrote:
> On Mon, Jul 18, 2022 at 3:51 AM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> >
> > drivers/platform/chrome/cros_kbd_led_backlight.c got a new build warning
> > when using the randconfig in [1]:
> > >>> warning: unused variable 'keyboard_led_drvdata_ec_pwm'
> >
> > The warning happens when CONFIG_CROS_EC is set but CONFIG_OF is not set.
> > Reproduce:
> > - mkdir build_dir
> > - wget [1] -O build_dir/.config
> > - COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 \
> >   O=build_dir ARCH=s390 SHELL=/bin/bash drivers/platform/chrome/
> >
> > Fix the warning by using __maybe_unused.  Also use IS_ENABLED() because
> > CROS_EC is a tristate.
> 
> Is that sufficient ? What happens if CROS_KBD_LED_BACKLIGHT=y and
> CROS_EC=m ? I suspect you might need IS_REACHABLE() instead of
> IS_ENABLED().

For current code, it's impossible to set CROS_KBD_LED_BACKLIGHT=y and
CROS_EC=m without setting ACPI=y.  Given that the dependencies:
CHROME_PLATFORMS [=y] && LEDS_CLASS [=y] && (ACPI [=n] || CROS_EC [=m]).

$ ./scripts/kconfig/merge_config.sh -n <(cat <<EOF
CONFIG_MODULES=y

CONFIG_NEW_LEDS=y
CONFIG_LEDS_CLASS=y

CONFIG_CHROME_PLATFORMS=y
CONFIG_CROS_EC=m
CONFIG_CROS_KBD_LED_BACKLIGHT=y
EOF
)
[...]
Value requested for CONFIG_CROS_KBD_LED_BACKLIGHT not in final .config
Requested value:  CONFIG_CROS_KBD_LED_BACKLIGHT=y
Actual value:     CONFIG_CROS_KBD_LED_BACKLIGHT=m


However, when ACPI=y, `keyboard_led_drvdata_ec_pwm` is unused.  Instead, it
uses `keyboard_led_drvdata_acpi` for current code.

I guess IS_ENABLED() is sufficient.  Does it make sense?