[PATCH 00/11] drm/panel: add a panel_bridge to every panel

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

This series makes every drm_panel create a drm_panel_bridge wrapping it, as
previously discussed [1][2].

A panel_bridge is currently created only afterwards by the component
accessing it (such as the previous bridge), but that creates a mismatch
between the panel and the panel_bridge lifetimes and devm ownership.

== Series outline

 1. The most common pattern for panel_bridge creation is:

      | drm_of_find_panel_or_bridge(..., &panel, &bridge);
      | if (panel)
      |     bridge = drm_panel_bridge_add();

    Adapt drm_of_find_panel_or_bridge() so it prioritizes the bridge, not
    the panel. With this small change all drivers using the above pattern
    get ready in advance for when every panel will have a bridge
    (a few commits below).

      drm: of: drm_of_find_panel_or_bridge: simplify freeing the remote node pointer
      drm: of: drm_of_find_panel_or_bridge: simplify error return paths
      drm: of: drm_of_find_panel_or_bridge: prioritize the bridge, not the panel

 2. Address circular module dependency that would arise in the following
    commit [RFC!]
 
      drm/panel: merge the drm_kms_helper module into the drm module

 3. The main commit

      drm/bridge: panel: add a panel_bridge to every panel

 4. After the previous commit, many drivers not using the pattern in (1.)
    will unconditionally create a second panel_bridge for the same panel.
    Being an RFC, fix *some* of them as an example; if the approach will
    be acked, all of them will be converted in a later iteration.
    
      drm/bridge: tc358767: don't create a panel_bridge
      drm/bridge: waveshare-dsi: don't create a panel_bridge
      drm/mcde: dsi: simplify device_node management using scoped for_each variant
      drm/mcde: dsi: don't create a panel_bridge
      drm/bridge: fsl-ldb: don't create a panel_bridge
      drm/bridge: samsung-dsim: don't create a panel_bridge

== Grand plan

This is part of the work to support hotplug of DRM bridges. The grand plan
was discussed in [0].

Here's the work breakdown (➜ marks the current series):

 1. ➜ add refcounting to DRM bridges struct drm_bridge,
      based on devm_drm_bridge_alloc()
    A. ✔ add new alloc API and refcounting (v6.16)
    B. ✔ convert all bridge drivers to new API (v6.17)
    C. ✔ kunit tests (v6.17)
    D. ✔ add get/put to drm_bridge_add/remove() + attach/detach()
         and warn on old allocation pattern (v6.17)
    E. ➜ add get/put on drm_bridge accessors
       1. ✔ drm_bridge_chain_get_first_bridge(), add cleanup action (v6.18)
       2. ✔ drm_bridge_get_prev_bridge() (v6.18)
       3. ✔ drm_bridge_get_next_bridge() (v6.19)
       4. ✔ drm_for_each_bridge_in_chain() (v6.19)
       5. ✔ drm_bridge_connector_init (v6.19)
       6. ✔ protect encoder bridge chain with a mutex (v7.2)
       7. ✔ of_drm_find_bridge
          a. ✔ add of_drm_get_bridge() (v7.0),
               convert basic direct users (v7.0-v7.1)
          b. ✔ convert direct of_drm_get_bridge() users, part 2 (v7.0)
          c. ✔ convert direct of_drm_get_bridge() users, part 3 (v7.0)
          d. ✔ convert direct of_drm_get_bridge() users, part 4 (v7.1-v7.2)
          e. ✔ bridge-only drm_of_find_panel_or_bridge() users (v7.2)
       8. ➜ panel_bridge lifetime
          a. … cleanup DRM_PANEL in bridge drivers
	  b. ➜ add a panel_bridge to every panel
       9. ✔ enforce drm_bridge_add before drm_bridge_attach (v6.19)
    F. ✔ debugfs improvements
       1. ✔ add top-level 'bridges' file (v6.16)
       2. ✔ show refcount and list lingering bridges (v6.19)
 2. ✔ handle gracefully atomic updates during bridge removal
    A. ✔ Add drm_bridge_enter/exit() to protect device resources (v7.0)
    B. ✔ Add drm_bridge_clear_and_put() (v7.1)
 3. … DSI host-device driver interaction
 4. ✔ removing the need for the "always-disconnected" connector
 5. ✔ Migrate i.MX LCDIF driver to bridge-connector (v7.2)
 6. … DRM bridge hotplug
    A. … Bridge hotplug management in the DRM core
       1. ✔ bridge-connector: attach encoder to the connector (v7.2)
       2. … drm bridge hotplug
    B.   Device tree description

[0] https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/#t

[1] https://lore.kernel.org/all/emuj2innmp6zmzd7pyakqzjqpdzhly6qfhakya3ydwmd63pl26@5jwxaidpikjw/
[2] https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-8-9d6f2c9c3058@bootlin.com/

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
Luca Ceresoli (11):
      drm: of: drm_of_find_panel_or_bridge: simplify freeing the remote node pointer
      drm: of: drm_of_find_panel_or_bridge: simplify error return paths
      drm: of: drm_of_find_panel_or_bridge: prioritize the bridge, not the panel
      drm/panel: merge the drm_kms_helper module into the drm module
      drm/bridge: panel: add a panel_bridge to every panel
      drm/bridge: tc358767: don't create a panel_bridge
      drm/bridge: waveshare-dsi: don't create a panel_bridge
      drm/mcde: dsi: simplify device_node management using scoped for_each variant
      drm/mcde: dsi: don't create a panel_bridge
      drm/bridge: fsl-ldb: don't create a panel_bridge
      drm/bridge: samsung-dsim: don't create a panel_bridge

 drivers/gpu/drm/Makefile               |  7 +++--
 drivers/gpu/drm/bridge/fsl-ldb.c       | 18 ++++---------
 drivers/gpu/drm/bridge/panel.c         | 47 +++++++++++++++++-----------------
 drivers/gpu/drm/bridge/samsung-dsim.c  | 19 +++-----------
 drivers/gpu/drm/bridge/tc358767.c      | 22 +++++-----------
 drivers/gpu/drm/bridge/waveshare-dsi.c | 16 ++++--------
 drivers/gpu/drm/drm_of.c               | 36 ++++++++++++--------------
 drivers/gpu/drm/drm_panel.c            |  3 +++
 drivers/gpu/drm/mcde/mcde_dsi.c        | 47 ++++++++--------------------------
 include/drm/drm_panel.h                |  8 ++++++
 10 files changed, 83 insertions(+), 140 deletions(-)
---
base-commit: c0f5782834718a69465a7169112062d4412856e4
change-id: 20260812-drm-bridge-every-panel-a1596d6efea4

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