This series shows removed bridges to the global <debugfs>/dri/bridges file.
Removed bridges are bridges after drm_bridges_remove() but before they are
eventually freed on the last drm_bridge_put().

This is part of the work towards removal of bridges from a still existing
DRM pipeline without use-after-free. The grand plan was discussed in [1].
Here's the work breakdown (➜ marks the current series):

This is part of the work towards removal of bridges from a still existing
DRM pipeline without use-after-free. The grand plan was discussed in [1].
Here's the work breakdown (➜ marks the current series):

 1. ➜ add refcounting to DRM bridges (struct drm_bridge)
    (based on devm_drm_bridge_alloc() [0])
    A. ✔ add new alloc API and refcounting (v6.16)
    B. ✔ convert all bridge drivers to new API (v6.17-rc1)
    C. ✔ kunit tests (v6.17-rc1)
    D. ✔ add get/put to drm_bridge_add/remove() + attach/detach()
         and warn on old allocation pattern (v6.17-rc1)
    E. … add get/put on drm_bridge accessors
       1. ✔ drm_bridge_chain_get_first_bridge() + add a cleanup action
            (drm-misc-next)
       2. ✔ drm_bridge_get_prev_bridge() (drm-misc-next)
       3. …✔ drm_bridge_get_next_bridge() (partially in drm-misc-next)
       4. …✔ drm_for_each_bridge_in_chain() (partially in drm-misc-next)
       5. drm_bridge_connector_init
       6. of_drm_find_bridge
       7. drm_of_find_panel_or_bridge, *_of_get_bridge
    F. ➜ debugfs improvements
       1. ✔ add top-level 'bridges' file (v6.16)
       2. ➜ show refcount and list removed bridges
 2. … handle gracefully atomic updates during bridge removal
 3. … DSI host-device driver interaction
 4. finish the hotplug bridge work, removing the "always-disconnected"
    connector, moving code to the core and potentially removing the
    hotplug-bridge itself (this needs to be clarified as points 1-3 are
    developed)

To show the removed bridges we need to keep track of them, thus add a new
global list to store them between drm_bridge_remove() and the eventual
free. This is bit tricky in case a bridge is removed and then re-added
before being freed. This is handled in patch 2.

This series  depends on one other series:
 * [PATCH v2 0/9] drm/bridge: get/put the bridge when looping over the encoder chain
   Link: https://lore.kernel.org/r/20250808-drm-bridge-alloc-getput-for_each_bridge-v2-0-edb6ee81edf1@bootlin.com
   Reason: trivial conflict in context (drm_for_each_bridge_in_chain_scoped())

[0] https://gitlab.freedesktop.org/drm/misc/kernel/-/commit/0cc6aadd7fc1e629b715ea3d1ba537ef2da95eec
[1] https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/t/#u

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
---
Changes in v8:
- Removed patch 1, now in drm-misc-next
- Renamed "removed" -> "lingering"
- Rewrote documentation changes to use "register" in lieu of "publish",
  split them to a separate patch
- Link to v7: https://lore.kernel.org/r/20250819-drm-bridge-debugfs-removed-v7-0-970702579978@bootlin.com

This series was initially part of v6 of this other series:
- Link to v6: https://lore.kernel.org/dri-devel/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/

---
Luca Ceresoli (3):
      drm/bridge: add list of removed refcounted bridges
      drm/debugfs: show removed bridges
      drm/bridge: adapt drm_bridge_add/remove() docs, mention the lingering list

 drivers/gpu/drm/drm_bridge.c | 46 ++++++++++++++++++++++++++++++++++++--------
 1 file changed, 38 insertions(+), 8 deletions(-)
---
base-commit: 27ed0d64a0f37224ca865fbf8f0aacdc46a3f481
change-id: 20250408-drm-bridge-debugfs-removed-2579f892e4b3

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

Hi,

On Fri, Sep 12, 2025 at 07:03:40PM +0200, Luca Ceresoli wrote:
> This series shows removed bridges to the global <debugfs>/dri/bridges file.
> Removed bridges are bridges after drm_bridges_remove() but before they are
> eventually freed on the last drm_bridge_put().
> 
> This is part of the work towards removal of bridges from a still existing
> DRM pipeline without use-after-free. The grand plan was discussed in [1].
> Here's the work breakdown (➜ marks the current series):
> 
> This is part of the work towards removal of bridges from a still existing
> DRM pipeline without use-after-free. The grand plan was discussed in [1].
> Here's the work breakdown (➜ marks the current series):
> 
>  1. ➜ add refcounting to DRM bridges (struct drm_bridge)
>     (based on devm_drm_bridge_alloc() [0])
>     A. ✔ add new alloc API and refcounting (v6.16)
>     B. ✔ convert all bridge drivers to new API (v6.17-rc1)
>     C. ✔ kunit tests (v6.17-rc1)
>     D. ✔ add get/put to drm_bridge_add/remove() + attach/detach()
>          and warn on old allocation pattern (v6.17-rc1)
>     E. … add get/put on drm_bridge accessors
>        1. ✔ drm_bridge_chain_get_first_bridge() + add a cleanup action
>             (drm-misc-next)
>        2. ✔ drm_bridge_get_prev_bridge() (drm-misc-next)
>        3. …✔ drm_bridge_get_next_bridge() (partially in drm-misc-next)
>        4. …✔ drm_for_each_bridge_in_chain() (partially in drm-misc-next)
>        5. drm_bridge_connector_init
>        6. of_drm_find_bridge
>        7. drm_of_find_panel_or_bridge, *_of_get_bridge
>     F. ➜ debugfs improvements
>        1. ✔ add top-level 'bridges' file (v6.16)
>        2. ➜ show refcount and list removed bridges
>  2. … handle gracefully atomic updates during bridge removal
>  3. … DSI host-device driver interaction
>  4. finish the hotplug bridge work, removing the "always-disconnected"
>     connector, moving code to the core and potentially removing the
>     hotplug-bridge itself (this needs to be clarified as points 1-3 are
>     developed)
> 
> To show the removed bridges we need to keep track of them, thus add a new
> global list to store them between drm_bridge_remove() and the eventual
> free. This is bit tricky in case a bridge is removed and then re-added
> before being freed. This is handled in patch 2.

Once the minor issue I've reported is fixed,
Reviewed-by: Maxime Ripard <mripard@kernel.org>

Maxime

Hi Maxime,

On Mon, 15 Sep 2025 10:13:16 +0200
Maxime Ripard <mripard@kernel.org> wrote:

> Once the minor issue I've reported is fixed,
> Reviewed-by: Maxime Ripard <mripard@kernel.org>

Ok, thanks!

v9 sent.

Note that this series depends on [0] which is waiting for discussion to
continue, so any feedback on drm_for_each_bridge_in_chain_scoped()
would be very welcome to unlock both this and other series from being
applied/sent.

[0]
https://lore.kernel.org/all/20250808-drm-bridge-alloc-getput-for_each_bridge-v2-3-edb6ee81edf1@bootlin.com/

Luca

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

On Mon, Sep 15, 2025 at 12:30:10PM +0200, Luca Ceresoli wrote:
> Hi Maxime,
> 
> On Mon, 15 Sep 2025 10:13:16 +0200
> Maxime Ripard <mripard@kernel.org> wrote:
> 
> > Once the minor issue I've reported is fixed,
> > Reviewed-by: Maxime Ripard <mripard@kernel.org>
> 
> Ok, thanks!
> 
> v9 sent.
> 
> Note that this series depends on [0] which is waiting for discussion to
> continue, so any feedback on drm_for_each_bridge_in_chain_scoped()
> would be very welcome to unlock both this and other series from being
> applied/sent.

Thanks for the reminder, I've reviewed it

Maxime