Message-Id: <20260107-drm-bridge-alloc-getput-drm_of_find_bridge-v4-0-a62b4399a6bf@bootlin.com>
Date: Wed, 07 Jan 2026 10:56:25 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Liu Ying <victor.liu@....com>, Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Shawn Guo <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, 
 Pengutronix Kernel Team <kernel@...gutronix.de>, 
 Fabio Estevam <festevam@...il.com>
Cc: Hui Pu <Hui.Pu@...ealthcare.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 dri-devel@...ts.freedesktop.org, imx@...ts.linux.dev, 
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Luca Ceresoli <luca.ceresoli@...tlin.com>
Subject: [PATCH v4 0/4] drm/bridge: add of_drm_find_and_get_bridge() and a
 managed *next_bridge, deprecate of_drm_find_bridge()

This v4 contains the leftovers of the v3 series that deprecated
of_drm_find_bridge(), added a replacement which handles bridge refcounting,
and converted some of the direct users. All patches have been applied
except the imx8qxp-pixel-link ones, which still need a review for the first
patch.

@Liu, patch 1 is waiting for a review and it's non-trivial, it would be
nice if you could have a look at that one at least.

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
       7. ➜ of_drm_find_bridge()
          a. ➜✔… add of_drm_get_bridge(), convert basic direct users
	         (v6.20?, one driver still pending)
	  b. convert other direct users
	  c. convert bridge-only drm_of_find_panel_or_bridge() users
       8. drm_of_find_panel_or_bridge, *_of_get_bridge
       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_dev_enter/exit() to protect device resources (v6.20?)
    B. … protect private_obj removal from list
 3. … DSI host-device driver interaction
 4. ✔ removing the need for the "always-disconnected" connector
 5. finish the hotplug bridge work, moving code to the core and potentially
    removing the hotplug-bridge itself (this needs to be clarified as
    points 1-3 are developed)

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

Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---
Changes in v4:
- Added review trailers
- Link to v3: https://lore.kernel.org/r/20251216-drm-bridge-alloc-getput-drm_of_find_bridge-v3-0-b5165fab8058@bootlin.com

Changes in v3:
- Completely rewrote using the __drm_bridge_free() idea to prevent
  use-after-free of the next_bridge for the common cases
- Added needed cleanups to the imx8qxp-pixel-link and imx8qxp-pxl2dpi
  drivers
- Removed various patches converting simple cases, to reduce the number of
  e-mails sent; will be moved to the follow-up series
- Link to v2: https://lore.kernel.org/r/20251128-drm-bridge-alloc-getput-drm_of_find_bridge-v2-0-88f8a107eca2@bootlin.com

Changes in v2:
- All patches: renamed drm_of_find_bridge() -> of_drm_get_bridge()
- Various fixes and improvements to patches 1-6, see individual patches
  changelog
- Removed bouncing recipient: Edmund Dea <edmund.j.dea@...el.com>
- Link to v1: https://lore.kernel.org/r/20251119-drm-bridge-alloc-getput-drm_of_find_bridge-v1-0-0db98a7fe474@bootlin.com

---
Luca Ceresoli (4):
      drm/bridge: imx8qxp-pixel-link: simplify logic to find next bridge
      drm/bridge: imx8qxp-pixel-link: simplify freeing of the remote device_node
      drm/bridge: imx8qxp-pixel-link: imx8qxp_pixel_link_find_next_bridge: return int, not ERR_PTR
      drm/bridge: imx8qxp-pixel-link: get/put the next bridge

 drivers/gpu/drm/bridge/imx/imx8qxp-pixel-link.c | 53 ++++++++++++-------------
 1 file changed, 25 insertions(+), 28 deletions(-)
---
base-commit: f12ad2e5233a1a30b3bd6fe1e784b3544caa2383
change-id: 20251117-drm-bridge-alloc-getput-drm_of_find_bridge-74903367448d

Best regards,
-- 
Luca Ceresoli <luca.ceresoli@...tlin.com>

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