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From:   Jani Nikula <jani.nikula@intel.com>
To:     Arnd Bergmann <arnd@arndb.de>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thierry Reding <thierry.reding@gmail.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Sam Ravnborg <sam@ravnborg.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, Sean Paul <sean@poorly.run>,
        dri-devel@lists.freedesktop.org,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Emil Velikov <emil.velikov@collabora.com>,
        Boris Brezillon <boris.brezillon@collabora.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/drm_panel: fix export of drm_panel_of_backlight, try #3
In-Reply-To: <20200107203231.920256-1-arnd@arndb.de>
Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
References: <20200107203231.920256-1-arnd@arndb.de>
Date:   Wed, 08 Jan 2020 11:55:29 +0200
Message-ID: <87zheyqnla.fsf@intel.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, 07 Jan 2020, Arnd Bergmann <arnd@arndb.de> wrote:
> Making this IS_REACHABLE() was still wrong, as that just determines
> whether the lower-level backlight code would be reachable from the panel
> driver. However, with CONFIG_DRM=y and CONFIG_BACKLIGHT_CLASS_DEVICE=m,
> the drm_panel_of_backlight is left out of drm_panel.o but the condition
> tells the driver that it is there, leading to multiple link errors such as
>
> ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-sitronix-st7701.ko] undefined!
> ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-sharp-ls043t1le01.ko] undefined!
> ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-seiko-43wvf1g.ko] undefined!
> ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-ronbo-rb070d30.ko] undefined!
> ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-rocktech-jh057n00900.ko] undefined!
> ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-panasonic-vvx10f034n00.ko] undefined!
> ERROR: "drm_panel_of_backlight" [drivers/gpu/drm/panel/panel-osd-osd101t2587-53ts.ko] undefined!
>
> Change the condition to check for whether the function was actually part
> of the drm module. This version of the patch survived a few hundred
> randconfig builds, so I have a good feeling this might be the last
> one for the export.

Broken record, this will still be wrong, even if it builds and links. No
backlight support for panel despite expectations.

See http://mid.mail-archive.com/87d0cnynst.fsf@intel.com

All of this is just another hack until the backlight config usage is
fixed for good. Do we really want to make this the example to copy paste
wherever we hit the issue next?

I'm not naking, but I'm not acking either.

BR,
Jani.


>
> Fixes: 4a34a9dcec94 ("drm/drm_panel: Fix EXPORT of drm_panel_of_backlight() one more time")
> Fixes: 907aa265fde6 ("drm/drm_panel: fix EXPORT of drm_panel_of_backlight")
> Fixes: 152dbdeab1b2 ("drm/panel: add backlight support")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  include/drm/drm_panel.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 121f7aabccd1..6193cb555acc 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -198,7 +198,8 @@ static inline struct drm_panel *of_drm_find_panel(const struct device_node *np)
>  }
>  #endif
>  
> -#if IS_REACHABLE(CONFIG_BACKLIGHT_CLASS_DEVICE)
> +#if IS_ENABLED(CONFIG_DRM_PANEL) && (IS_BUILTIN(CONFIG_BACKLIGHT_CLASS_DEVICE) || \
> +	(IS_MODULE(CONFIG_DRM) && IS_MODULE(CONFIG_BACKLIGHT_CLASS_DEVICE)))
>  int drm_panel_of_backlight(struct drm_panel *panel);
>  #else
>  static inline int drm_panel_of_backlight(struct drm_panel *panel)

-- 
Jani Nikula, Intel Open Source Graphics Center