linux-kernel - Re: [PATCH] drm/drm_panel: fix export of drm_panel_of

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Date:   Sun, 12 Jan 2020 21:22:07 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Sean Paul <sean@...rly.run>, dri-devel@...ts.freedesktop.org,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Emil Velikov <emil.velikov@...labora.com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Jani Nikula <jani.nikula@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/drm_panel: fix export of drm_panel_of_backlight, try
 #3

Hi Arnd.

On Tue, Jan 07, 2020 at 09:32:19PM +0100, Arnd Bergmann 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.
> 
> 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@...db.de>

I spent some hours this weekend trying to improve the Kconfig
logic around BACKLIGHT_CLASS_DEVICE and ACPI_VIDEO.

I did manage to change something but I did not manage to make something
that is a real improvement to the current situation.
So everything abandoned.

As we need this fixed I have applied your patch to drm-misc-next.
Thanks,

	Sam

> ---
>  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)
> -- 
> 2.20.0