[PATCH] drm/drm_panel: fix export of drm_panel_of_backlight, try #3

[Arnd Bergmann]

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@xxxxxxxx>
---
 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