Re: [PATCH] drm/panel: select DRM_KMS_HELPER

[Luca Ceresoli]

On Tue Sep 29, 2026 at 1:48 PM CEST, Sasha Levin wrote:
> Since the panel_bridge code moved into drm_panel.c, any config with
> DRM built in but without the KMS helpers fails to link, for example
> arc haps_hs_smp_defconfig with allnoconfig and the kselftest fragment:
>
>   arc-elf32-ld: drivers/gpu/drm/drm_panel.o:(.rodata+0x28): undefined
>   reference to `drm_atomic_helper_bridge_duplicate_state'
>   arc-elf32-ld: drivers/gpu/drm/drm_panel.o:(.rodata+0x2c): undefined
>   reference to `drm_atomic_helper_bridge_destroy_state'
>   ...
>
> With DRM=m, modpost fails the same way:
>
>   ERROR: modpost: drivers/gpu/drm/drm_panel.ko: symbol
>   'drm_atomic_helper_bridge_duplicate_state' undefined!
>
> The panel_bridge used to live in bridge/panel.c, which was part of
> drm_kms_helper and was therefore only built when DRM_KMS_HELPER was
> enabled. drm_panel.c is built for DRM_PANEL instead, which
> DRM_PANEL_BRIDGE selects whenever DRM_BRIDGE is set, and DRM_BRIDGE
> is enabled for every DRM config. Nothing on that path selects
> DRM_KMS_HELPER, so the bridge and connector helpers used by the moved
> code can be missing.
>
> The panel_bridge code in drm_panel.c is built unconditionally, so
> make DRM_PANEL select DRM_KMS_HELPER.
>
> Reported-by: kernelci.org bot <bot@xxxxxxxxxxxx>
> Closes: https://d.kernelci.org/i/maestro:9ed7f4b210fa7c1d3bb109b0fcd62285e98c5b81
> Fixes: aa8a8c7e4641 ("drm/bridge: panel: move all code to drm_panel.c")
> Assisted-by: LLM
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

Reviewed-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>
Tested-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com