[PATCH RFC v2 00/24] drm bridge hotplug

[Luca Ceresoli]

Hello,

this series adds support for Linux-based devices with a DRM pipeline whose
final components, including one or more bridges, can be hot-plugged and
hot-unplugged

For more about the use case see the v1 cover letter:
https://lore.kernel.org/lkml/20260519-drm-bridge-hotplug-v1-0-45e2bdb3dfb4@xxxxxxxxxxx/

For reviewers with limited time for review
==========================================

These are the patches with the core changes and likely needing review and
discussion (most relevant first):

 * 23: the new drm_hotplug_helper (the main patch)
 * 24: an example usage
 * 5-6: the main changes to the bridge-connector
 * 17-22: the new get_next_bridge bridge func

The following can be skipped at this iteration, changes have been requested
in the v1 discussion but not yet implemented, and these patches are not
crucial:

 * 10-12: still needs rewording
 * 13-16: need docs, still todo

Design
======

The drm_bridge_connector is nowadays the recommended way to implement DRM
connectors when a chain of bridges is used.

This series proposes a small helper (drm_hotplug_helper) which drivers can
use to make their encoder able to:

 * receive hotplug-relevant events
 * add a drm_bridge_connector when a new bridge is added making the
   pipeline complete in the hardware
 * remove the drm_bridge_connector when a bridge is removed
 
Series layout
=============

 A. Add a dynamic variant of drmm_connector_hdmi_init()
    (needed for the bridge-connector to allocate the connector dynamically)

      1 drm/connector: split drmm_connector_hdmi_init() in 3 parts
      2 drm/connector: add drm_connector_hdmi_dynamic_init()

 B. bridge-connector: use a dynamic drm_connector

      3 drm/display: bridge-connector: split code allocation from initialization
      4 drm/display: bridge-connector: hoist error management to common code
      5 drm/display: bridge-connector: use a dynamic connector
      6 drm/display: bridge-connector: add APIs to add/remove the connector dynamically

 C. Misc preparation work

      7 drm/bridge: samsung-dsim: move drm_bridge_add() call to probe
      8 drm/bridge: initialize chain_node list head on allocation
      9 drm/bridge: initialize chain_node list head on detach and attach errors

 D. drm_bridge: stop pipeline when a bridge is removed

     10 drm/encoder: add drm_encoder_cleanup_from()
     11 drm/atomic: move drm_atomic_helper_disable_all() and drm_atomic_helper_shutdown() from drm_atomic_helper to drm_atomic
     12 drm/bridge: shutdown and cleanup on bridge unplug

 E. Add notifier mechanism to let common code (the bridge-connector)
    take actions on hotplug events

     13 drm/mipi-dsi: turn DRM_MIPI_DSI into a tristate
     14 drm: event-notifier: add mechanism to notify about hotplug events
     15 drm/bridge: notify about detached bridges
     16 drm/mipi-dsi: notify about DSI attach

 F. Let bridges return their next bridge
    (allows to know when the pipeline is complete)

     17 drm/bridge: add drm_bridge_get_next() and supporting func
     18 drm/panel: implement .get_next_bridge
     19 drm/bridge: display-connector: implement .get_next_bridge
     20 drm/bridge: ti-sn65dsi83: implement .get_next_bridge
     21 drm/bridge: ti-sn65dsi86: implement .get_next_bridge
     22 drm/bridge: samsung-dsim: implement .get_next_bridge

 G. Implement bridge hotplug in bridge-connector, enable it in a driver

     23 drm: drm_hotplug_helper: new helper to implement bridge hotplug
     24 drm/mxsfb/lcdif: enable bridge hotplug

== Grand plan

This is part of the work to support hotplug of DRM bridges. The grand plan
was initially 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 (v7.4)
	  b. ✔ embed a drm_bridge in every drm_panel (v7.4)
	  c. … remove deprecated *_of_get_bridge(): non-OF drivers
	  d.   remove deprecated *_of_get_bridge(): OF drivers
       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@xxxxxxxxxxx/#t
   

---
Changes in v2:
- Rewrote: added new drm_hotplug_helper, dropped most changes to drm_bridge_connector
- Added get_next_bridge func, dropped is_tail func
- Rebased on drm-misc-next, which required a few reworks
- Fix dynconn mutex locking
- Fix sashiko-reported bugs
- Drop "drm/display: bridge-connector: store the drm_device pointer", not
  strongly needed, and adapt the remaining patches
- Simplify handle_hpd code types
- Lots of other smaller improvements
- Link to v1: https://patch.msgid.link/20260519-drm-bridge-hotplug-v1-0-45e2bdb3dfb4@xxxxxxxxxxx

---
Luca Ceresoli (24):
      drm/connector: split drmm_connector_hdmi_init() in 3 parts
      drm/connector: add drm_connector_hdmi_dynamic_init()
      drm/display: bridge-connector: split code allocation from initialization
      drm/display: bridge-connector: hoist error management to common code
      drm/display: bridge-connector: use a dynamic connector
      drm/display: bridge-connector: add APIs to add/remove the connector dynamically
      drm/bridge: samsung-dsim: move drm_bridge_add() call to probe
      drm/bridge: initialize chain_node list head on allocation
      drm/bridge: initialize chain_node list head on detach and attach errors
      drm/encoder: add drm_encoder_cleanup_from()
      drm/atomic: move drm_atomic_helper_disable_all() and drm_atomic_helper_shutdown() from drm_atomic_helper to drm_atomic
      drm/bridge: shutdown and cleanup on bridge unplug
      drm/mipi-dsi: turn DRM_MIPI_DSI into a tristate
      drm: event-notifier: add mechanism to notify about hotplug events
      drm/bridge: notify about detached bridges
      drm/mipi-dsi: notify about DSI attach
      drm/bridge: add drm_bridge_get_next() and supporting func
      drm/panel: implement .get_next_bridge
      drm/bridge: display-connector: implement .get_next_bridge
      drm/bridge: ti-sn65dsi83: implement .get_next_bridge
      drm/bridge: ti-sn65dsi86: implement .get_next_bridge
      drm/bridge: samsung-dsim: implement .get_next_bridge
      drm: drm_hotplug_helper: new helper to implement bridge hotplug
      drm/mxsfb/lcdif: enable bridge hotplug

 MAINTAINERS                                    |   8 +
 drivers/gpu/drm/Kconfig                        |   7 +-
 drivers/gpu/drm/Makefile                       |   2 +
 drivers/gpu/drm/bridge/display-connector.c     |   7 +
 drivers/gpu/drm/bridge/samsung-dsim.c          |  24 ++-
 drivers/gpu/drm/bridge/ti-sn65dsi83.c          |   9 +
 drivers/gpu/drm/bridge/ti-sn65dsi86.c          |  11 +-
 drivers/gpu/drm/display/Kconfig                |   6 +
 drivers/gpu/drm/display/Makefile               |   2 +
 drivers/gpu/drm/display/drm_bridge_connector.c | 172 +++++++++++------
 drivers/gpu/drm/display/drm_hotplug_helper.c   | 243 +++++++++++++++++++++++++
 drivers/gpu/drm/drm_atomic.c                   | 115 ++++++++++++
 drivers/gpu/drm/drm_atomic_helper.c            |  76 +-------
 drivers/gpu/drm/drm_bridge.c                   |  45 ++++-
 drivers/gpu/drm/drm_connector.c                | 130 +++++++++----
 drivers/gpu/drm/drm_encoder.c                  |  38 ++++
 drivers/gpu/drm/drm_event_notifier.c           |  58 ++++++
 drivers/gpu/drm/drm_mipi_dsi.c                 |   3 +
 drivers/gpu/drm/drm_panel.c                    |   8 +-
 drivers/gpu/drm/mxsfb/Kconfig                  |   2 +-
 drivers/gpu/drm/mxsfb/lcdif_drv.c              |  12 +-
 include/drm/drm_atomic.h                       |   3 +
 include/drm/drm_bridge.h                       |  26 +++
 include/drm/drm_bridge_connector.h             |   4 +
 include/drm/drm_connector.h                    |   6 +
 include/drm/drm_encoder.h                      |   1 +
 include/drm/drm_event_notifier.h               |  38 ++++
 include/drm/drm_hotplug_helper.h               |  13 ++
 28 files changed, 894 insertions(+), 175 deletions(-)
---
base-commit: e051645b3b4be7c8f9f77596e62f554cd52b008b
change-id: 20260515-drm-bridge-hotplug-46265d3a2f85

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