Re: [PATCH] drm: Don't make DRM_PANEL_BRIDGE dependent on DRM_KMS_HELPERS

[Brian Masney <bmasney@redhat.com>]

On Tue, Mar 15, 2022 at 09:45:59AM +0100, Thomas Zimmermann wrote:
> Fix a number of undefined references to drm_kms_helper.ko in
> drm_dp_helper.ko:
> 
>   arm-suse-linux-gnueabi-ld: drivers/gpu/drm/dp/drm_dp_mst_topology.o: in function `drm_dp_mst_duplicate_state':
>   drm_dp_mst_topology.c:(.text+0x2df0): undefined reference to `__drm_atomic_helper_private_obj_duplicate_state'
>   arm-suse-linux-gnueabi-ld: drivers/gpu/drm/dp/drm_dp_mst_topology.o: in function `drm_dp_delayed_destroy_work':
>   drm_dp_mst_topology.c:(.text+0x370c): undefined reference to `drm_kms_helper_hotplug_event'
>   arm-suse-linux-gnueabi-ld: drivers/gpu/drm/dp/drm_dp_mst_topology.o: in function `drm_dp_mst_up_req_work':
>   drm_dp_mst_topology.c:(.text+0x7938): undefined reference to `drm_kms_helper_hotplug_event'
>   arm-suse-linux-gnueabi-ld: drivers/gpu/drm/dp/drm_dp_mst_topology.o: in function `drm_dp_mst_link_probe_work':
>   drm_dp_mst_topology.c:(.text+0x82e0): undefined reference to `drm_kms_helper_hotplug_event'
> 
> This happens if panel-edp.ko has been configured with
> 
>   DRM_PANEL_EDP=y
>   DRM_DP_HELPER=y
>   DRM_KMS_HELPER=m
> 
> which builds DP helpers into the kernel and KMS helpers sa a module.
> Making DRM_PANEL_EDP select DRM_KMS_HELPER resolves this problem.
> 
> To avoid a resulting cyclic dependency with DRM_PANEL_BRIDGE, don't
> make the latter depend on DRM_KMS_HELPER and fix the one DRM bridge
> drivers that doesn't already select DRM_KMS_HELPER. As KMS helpers
> cannot be selected directly by the user, config symbols should avoid
> depending on it anyway.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Fixes: 3755d35ee1d2 ("drm/panel: Select DRM_DP_HELPER for DRM_PANEL_EDP")
> Reported-by: kernel test robot <lkp@intel.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Naresh Kamboju <naresh.kamboju@linaro.org>
> Cc: Linux Kernel Functional Testing <lkft@linaro.org>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Maxime Ripard <mripard@kernel.org>
> Cc: dri-devel@lists.freedesktop.org
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: Thierry Reding <thierry.reding@gmail.com>

This patch fixes the build error that I see with qcom_defconfig in
linux-next.

Tested-by: Brian Masney <bmasney@redhat.com>