[PATCH v2] drm/panel: Select DRM_DP_HELPER for DRM_PANEL_EDP

[Thomas Zimmermann]

As reported in [1], DRM_PANEL_EDP depends on DRM_DP_HELPER. Select
the option to fix the build failure. The error message is shown
below.

  arm-linux-gnueabihf-ld: drivers/gpu/drm/panel/panel-edp.o: in function
    `panel_edp_probe': panel-edp.c:(.text+0xb74): undefined reference to
    `drm_panel_dp_aux_backlight'
  make[1]: *** [/builds/linux/Makefile:1222: vmlinux] Error 1

The issue has been reported before, when DisplayPort helpers were
hidden behind the option CONFIG_DRM_KMS_HELPER. [2]

v2:
	* fix and expand commit description (Arnd)

Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
Fixes: adb9d5a2cc77 ("drm/dp: Move DisplayPort helpers into separate helper module")
Fixes: 5f04e7ce392d ("drm/panel-edp: Split eDP panels out of panel-simple")
Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>
Link: https://lore.kernel.org/dri-devel/CA+G9fYvN0NyaVkRQmA1O6rX7H8PPaZrUAD7=RDy33QY9rUU-9g@xxxxxxxxxxxxxx/ # [1]
Link: https://lore.kernel.org/all/20211117062704.14671-1-rdunlap@xxxxxxxxxxxxx/ # [2]
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: Lyude Paul <lyude@xxxxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
---
 drivers/gpu/drm/panel/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/panel/Kconfig b/drivers/gpu/drm/panel/Kconfig
index 434c2861bb40..0aec5a10b064 100644
--- a/drivers/gpu/drm/panel/Kconfig
+++ b/drivers/gpu/drm/panel/Kconfig
@@ -106,6 +106,7 @@ config DRM_PANEL_EDP
 	depends on PM
 	select VIDEOMODE_HELPERS
 	select DRM_DP_AUX_BUS
+	select DRM_DP_HELPER
 	help
 	  DRM panel driver for dumb eDP panels that need at most a regulator and
 	  a GPIO to be powered up. Optionally a backlight can be attached so
-- 
2.34.1