The DRM_DP_AUX_CHARDEV and DRM_DP_CEC boolean Kconfig symbols enable code that use DP helper functions, exported by the display-helper module.

But these don't select the DRM_DISPLAY_DP_HELPER and DRM_DISPLAY_HELPER symbols, to make sure that the functions used will be present. This leads to the following linking errors if CONFIG_DRM_DISPLAY_HELPER is set to m:

LD vmlinux.o MODPOST vmlinux.symvers MODINFO modules.builtin.modinfo GEN modules.builtin LD .tmp_vmlinux.kallsyms1 KSYMS .tmp_vmlinux.kallsyms1.S AS .tmp_vmlinux.kallsyms1.S LD .tmp_vmlinux.kallsyms2 KSYMS .tmp_vmlinux.kallsyms2.S AS .tmp_vmlinux.kallsyms2.S LD vmlinux SYSMAP System.map SORTTAB vmlinux OBJCOPY arch/arm64/boot/Image MODPOST modules-only.symvers ERROR: modpost: "drm_dp_dpcd_write" [drivers/gpu/drm/display/drm_display_helper.ko] undefined! ERROR: modpost: "drm_dp_read_desc" [drivers/gpu/drm/display/drm_display_helper.ko] undefined! ERROR: modpost: "drm_dp_dpcd_read" [drivers/gpu/drm/display/drm_display_helper.ko] undefined! make[1]: *** [scripts/Makefile.modpost:134: modules-only.symvers] Error 1 make[1]: *** Deleting file 'modules-only.symvers' make: *** [Makefile:1749: modules] Error 2

Note: It seems this has been an issue for a long time but was made easier to reproduce after the commit 1e0f66420b13 ("drm/display: Introduce a DRM display-helper module"). Adding a Fixes: tag just to make sure that this fix will be picked for stable once the mentioned change also lands there.

Fixes: 1e0f66420b13 ("drm/display: Introduce a DRM display-helper module") Signed-off-by: Javier Martinez Canillas javierm@redhat.com ---

drivers/gpu/drm/display/Kconfig | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/display/Kconfig b/drivers/gpu/drm/display/Kconfig index f84f1b0cd23f..d7a413a2c6cc 100644 --- a/drivers/gpu/drm/display/Kconfig +++ b/drivers/gpu/drm/display/Kconfig @@ -32,6 +32,8 @@ config DRM_DISPLAY_HDMI_HELPER config DRM_DP_AUX_CHARDEV bool "DRM DP AUX Interface" depends on DRM + select DRM_DISPLAY_DP_HELPER + select DRM_DISPLAY_HELPER help Choose this option to enable a /dev/drm_dp_auxN node that allows to read and write values to arbitrary DPCD registers on the DP aux @@ -40,6 +42,8 @@ config DRM_DP_AUX_CHARDEV config DRM_DP_CEC bool "Enable DisplayPort CEC-Tunneling-over-AUX HDMI support" depends on DRM + select DRM_DISPLAY_DP_HELPER + select DRM_DISPLAY_HELPER select CEC_CORE help Choose this option if you want to enable HDMI CEC support for