Re: [PATCH 04/11] drm/panel: merge the drm_kms_helper module into the drm module

[Maxime Ripard]

On Mon, Aug 17, 2026 at 02:27:58PM +0200, Luca Ceresoli wrote:
> On Mon Aug 17, 2026 at 10:31 AM CEST, Maxime Ripard wrote:
> > On Fri, Aug 14, 2026 at 04:05:52PM +0200, Luca Ceresoli wrote:
> >> Work is in progress to make every drm_panel automatically create a
> >> panel_bridge [0][1].
> >>
> >> This requires the panel code to call the drm_panel_bridge APIs. However
> >> this would create a circular dependency loop on modular builds:
> >>
> >> __devm_drm_panel_alloc() [drm]
> >>    -> drm_panel_bridge_add() [drm_kms_helper]
> >>       -> drm_bridge.c APIs [drm]
> >>
> >> Moving just the panel_brige.o file from [drm_kms_helper] to [drm] does not
> >> work because the panel bridge code uses the drm_atomic_helper and
> >> drm_probe_helper which add further dependencies on symbols in the
> >> [drm_kms_helper] module.
> >>
> >> So take a simple approach, and move the entire drm_kms_helper into the
> >> [drm] module.
> >>
> >> Link: https://lore.kernel.org/all/emuj2innmp6zmzd7pyakqzjqpdzhly6qfhakya3ydwmd63pl26@5jwxaidpikjw/ [0]
> >> Link: https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-8-9d6f2c9c3058@xxxxxxxxxxx/ [1]
> >> Signed-off-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>
> >
> > So, that's not an option. However, why do we need drm_panel_bridge_add()
> > after this work is done? If we want to create a bridge for every panel,
> > then the bridge implementation can live in drm_panel.c, which is part of
> > the drm module.
> >
> > And we'd essentially move drm_panel_bridge into drm_panel.c, and make it
> > private.
> 
> Yes in theory, but the panel_bridge code uses other parts of the
> drm_kms_helper module: drm_atomic_helper and drm_probe_helper, maybe more,
> so we'd have to move them into the drm module too.

Ah, right. What would happen if we were doing it the other way around
then? Move drm_panel out of the main drm module?

> Is it worth trying to identify only the closure of files in drm_kms_helpers
> that are actually used by the panel_bridg, and move only them? That'd mean
> having some *_helper.c files in the drm module and other *_helper.c files
> in the drm module.
> 
> There's a licensing aspect too: drm_panel.c is MIT-licensed, bridge/panel.c
> is GPL-2.0-or-later. However my understanding is that we can merge the two
> into a single file and the result would all be GPL-2.0-or-later, so that is
> an option.

Yeah, that's not a concern.

Maxime

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