Re: [PATCH v2 0/9] drm/bridge: get/put the bridge returned by drm_bridge_get_next_bridge()

[Liu Ying <victor.liu@nxp.com>]

Hi Luca,

On 08/01/2025, Luca Ceresoli wrote:
> Note: the cover in v1 was mentioning by mistake
> drm_bridge_get_last_bridge() instead of drm_bridge_get_next_bridge().
>                ^^^^
> 
> This series adds drm_bridge_get/put() calls for DRM bridges returned by
> drm_bridge_get_next_bridge().
> 
> 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 (in v6.16-rc1)
>     B. ✔ convert all bridge drivers to new API (now in drm-misc-next)
>     C. ✔ kunit tests (now in drm-misc-next)
>     D. ✔ add get/put to drm_bridge_add/remove() + attach/detach()
>          and warn on old allocation pattern (now in drm-misc-next)
>     E. ➜ add get/put on drm_bridge accessors
>        1. ✔ drm_bridge_chain_get_first_bridge() + add a cleanup action
>        2. ✔ drm_bridge_get_prev_bridge()
>        3. ➜ drm_bridge_get_next_bridge()
>        4. … drm_for_each_bridge_in_chain()
>        5. drm_bridge_connector_init
>        6. of_drm_find_bridge
>        7. drm_of_find_panel_or_bridge, *_of_get_bridge
>     F. debugfs improvements
>  2. handle gracefully atomic updates during bridge removal
>  3. … avoid DSI host drivers to have dangling pointers to DSI devices
>  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)
> 
> There are various users of drm_bridge_get_next_bridge() which cannot be
> converted easily. Luckily they are not really looking for the next bridge,
> but for something else, such as getting the last bridge in the encoder
> chain or checking whether a bridge is the last in the encoder chain. So
> introduce better functions for those users and use them instead of
> drm_bridge_get_next_bridge(), making the code cleaner at the same time.
> 
> Finally add a drm_bridge_get() to drm_bridge_get_next_bridge() and
> drm_bridge_put() to the remaining, and legitimate, calls.
> 
> [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 v2:
> - Use cleanup action in patches 4, 8 and 9
> - Fix: replace get_last -> get_next in cover
> - Link to v1: https://lore.kernel.org/r/20250709-drm-bridge-alloc-getput-drm_bridge_get_next_bridge-v1-0-48920b9cf369@bootlin.com
> 
> ---
> Luca Ceresoli (9):
>       list: add list_last_entry_or_null()
>       drm/bridge: add drm_bridge_chain_get_last_bridge()
>       drm/bridge: imx93-mipi-dsi: use drm_bridge_chain_get_last_bridge()
>       drm/omapdrm: use drm_bridge_chain_get_last_bridge()
>       drm/bridge: add drm_bridge_is_last()
>       drm/display: bridge_connector: use drm_bridge_is_last()
>       drm/bridge: get the bridge returned by drm_bridge_get_next_bridge()
>       drm/bridge: put the bridge returned by drm_bridge_get_next_bridge()
>       drm/imx: parallel-display: put the bridge returned by drm_bridge_get_next_bridge()
> 
>  drivers/gpu/drm/bridge/imx/imx93-mipi-dsi.c    | 12 ++++------
>  drivers/gpu/drm/display/drm_bridge_connector.c |  5 ++--
>  drivers/gpu/drm/drm_bridge.c                   |  3 +--
>  drivers/gpu/drm/imx/ipuv3/parallel-display.c   |  4 ++--
>  drivers/gpu/drm/omapdrm/omap_drv.c             |  6 ++---
>  include/drm/drm_bridge.h                       | 32 +++++++++++++++++++++++++-
>  include/linux/list.h                           | 14 +++++++++++
>  7 files changed, 57 insertions(+), 19 deletions(-)

Looks like this one needs to be handled by this patch series?

drivers/gpu/drm/omapdrm/omap_encoder.c:101:
bridge = drm_bridge_get_next_bridge(bridge)) {

> ---
> base-commit: b13c47e0f6f5a7be56ed93d596f80eb9d8e12c77
> change-id: 20250709-drm-bridge-alloc-getput-drm_bridge_get_next_bridge-1df6aaf62136
> 
> Best regards,


-- 
Regards,
Liu Ying