drm/panel: embed a drm_bridge into every drm_panel

Adding a drm_panel does currently not add a panel_bridge wrapping
it. Usually the panel_bridge creation happens later, when some other driver
(e.g. the previous bridge or the encoder) calls *_of_get_bridge() and the
following element in the pipeline is a panel.

This has some drawbacks:

 * the bridge API is currently the best practice to access various
   components of the pipeline, especially with complex cards where bridges
   can be combined in different ways on different hardware
 * the panel_bridge is not created in the context of the driver of the
   underlying physical device (the panel driver), but of some other driver
 * that other driver is not aware of whether the returned drm_bridge
   pointer is a panel_bridge created on the fly, a pre-existing
   panel_bridge or a non-panel bridge
 * removal of a panel_bridge requires calling drm_panel_bridge_remove(),
   but that other driver doesn't know whether this is needed because it
   doesn't know whether it has created a panel_bridge or not

Other drivers call [a variant of] drm_panel_bridge_add(), which also has
some of the above drawbacks.

So far the current approach was working mostly because devm and drmm ensure
the panel bridge would be dealloacted at some later point. However with the
upcoming implementation of bridge hotplug and dynamic bridge lifetime this
won't happen as needed.

Switch to the new approach: embed a drm_bridge inside every drm_panel,
which behaves just like the current drm_panel_bridge. Do this by adapting
the panel_bridge code, doing the minimal adaptations needed.

Currently drm_bridge and drm_panel have independent refcounted
allocation. As they now become a single struct, just change
drm_panel_get/put() to get/put the bridge. As a result, the refcount for a
drm_bridge embedded in a drm_panel is:

  bridge.refcount == number of drm_bridge_get() calls
                   + number of drm_panel_get() calls
                   - number of drm_bridge_put() calls
                   - number of drm_panel_put() calls

Now drivers should progressively stop using the panel_bridge API. Until
that happens, that API becomes now a wrapper to the new embedded
drm_bridge:

 * drm_panel_bridge_add() and derivatives don't create a bridge, they
   just drm_bridge_get() and return a pointer to the existing one
 * drm_panel_bridge_remove() and devm_drm_panel_bridge_release() don't
   remove the bridge, they just drm-bridge_put() it
 * The other panel_bridge functions stack on those listed in the previous 2
   bullets, so their behaviour is changed correspondingly; they include:
   - all drm_panel_bridge_add() variants
   - their removal counterparts
   - *_of_get_bridge().

Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://patch.msgid.link/20260916-drm-bridge-every-panel-v3-5-83afb4f1a707@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

0 files changed, 0 insertions, 0 deletions