[PATCH 4.17 213/324] drm/sun4i: link in front-end code if needed

[Greg Kroah-Hartman]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Arnd Bergmann <arnd@xxxxxxxx>

[ Upstream commit 3156b53c2e2fadafa1a16412a8791b38f94b5bdc ]

When the base sun4i DRM driver is built-in but the back-end is
a loadable module, we run into a link error:

drivers/gpu/drm/sun4i/sun4i_drv.o: In function `sun4i_drv_probe':
sun4i_drv.c:(.text+0x60c): undefined reference to `sun4i_frontend_of_table'

The dependency is a bit tricky, the best workaround I have come up
with is to use a Makefile hack to to interpret both
CONFIG_DRM_SUN4I_BACKEND=m and CONFIG_DRM_SUN4I_BACKEND=y
as a directive to build the front-end the same way as the main module.

Fixes: dd0421f47505 ("drm/sun4i: Add a driver for the display frontend")
Link: https://lore.kernel.org/lkml/20180301091908.zcptz3ezqr2c6ly5@flea/
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20180706142847.2032381-1-arnd@xxxxxxxx
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/sun4i/Makefile |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/sun4i/Makefile
+++ b/drivers/gpu/drm/sun4i/Makefile
@@ -29,7 +29,10 @@ obj-$(CONFIG_DRM_SUN4I)		+= sun4i-tcon.o
 obj-$(CONFIG_DRM_SUN4I)		+= sun4i_tv.o
 obj-$(CONFIG_DRM_SUN4I)		+= sun6i_drc.o
 
-obj-$(CONFIG_DRM_SUN4I_BACKEND)	+= sun4i-backend.o sun4i-frontend.o
+obj-$(CONFIG_DRM_SUN4I_BACKEND)	+= sun4i-backend.o
+ifdef CONFIG_DRM_SUN4I_BACKEND
+obj-$(CONFIG_DRM_SUN4I)		+= sun4i-frontend.o
+endif
 obj-$(CONFIG_DRM_SUN4I_HDMI)	+= sun4i-drm-hdmi.o
 obj-$(CONFIG_DRM_SUN8I_DW_HDMI)	+= sun8i-drm-hdmi.o
 obj-$(CONFIG_DRM_SUN8I_MIXER)	+= sun8i-mixer.o