| Message ID | 20250314-drm-bridge-refcount-v7-0-152571f8c694@bootlin.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | drm/bridge: add devm_drm_bridge_alloc() with bridge refcount | expand |
Hi, On Fri, Mar 14, 2025 at 11:31:13AM +0100, Luca Ceresoli wrote: > This series improves the way DRM bridges are allocated and initialized and > makes them reference-counted. The goal of reference counting is to avoid > use-after-free by drivers which got a pointer to a bridge and keep it > stored and used even after the bridge has been deallocated. > > The overall goal is supporting Linux devices with a DRM pipeline whose > final components can be hot-plugged and hot-unplugged, including one or > more bridges. For more details see the big picture [0]. > > DRM bridge drivers will have to be adapted to the new API, which is pretty > simple for most cases. Refcounting will have to be adopted on the two > sides: all functions returning a bridge pointer and all code obtaining such > a pointer. This series has just an overview of some of those conversions, > because for now the main goal is to agree on the API. > > Series layout: > > 1. Add the new API and refcounting: > > drm/bridge: add devm_drm_bridge_alloc() > drm/bridge: add support for refcounting > > 2. get/put the reference in basic operations in the bridge core: > > drm/bridge: get/put the bridge reference in drm_bridge_add/remove() > drm/bridge: get/put the bridge reference in drm_bridge_attach/detach() > > 3. as an example of changes for bridge consumers, get a reference for the > bridge returned by drm_bridge_chain_get_first_bridge(), have it put by > all callers (all users will be covered later on separately): > > drm/bridge: add a cleanup action for scope-based drm_bridge_put() invocation > drm/bridge: get the bridge returned by drm_bridge_chain_get_first_bridge() > drm/mxsfb: put the bridge returned by drm_bridge_chain_get_first_bridge() > drm/atomic-helper: put the bridge returned by drm_bridge_chain_get_first_bridge() > drm/probe-helper: put the bridge returned by drm_bridge_chain_get_first_bridge() > > 4. convert a few bridge drivers (bridge providers) to the new API: > > drm/bridge: ti-sn65dsi83: use dynamic lifetime management > drm/bridge: samsung-dsim: use dynamic lifetime management > > This work was formerly a part of my v6 DRM bridge hotplug series[0], now > split as a standalone series with many improvements, hence the "v7" version > number. Except for one patch where I had comments, I think the series is in excellent shape. We're still missing a couple of things to close this topic though: - Converting the other bridge iterators/accessors to take / put the references - Mass converting the drivers to devm_drm_bridge_alloc - Documenting somewhere (possibly in drm_bridge_init?) that it really shouldn't be used anymore Maxime
This series improves the way DRM bridges are allocated and initialized and makes them reference-counted. The goal of reference counting is to avoid use-after-free by drivers which got a pointer to a bridge and keep it stored and used even after the bridge has been deallocated. The overall goal is supporting Linux devices with a DRM pipeline whose final components can be hot-plugged and hot-unplugged, including one or more bridges. For more details see the big picture [0]. DRM bridge drivers will have to be adapted to the new API, which is pretty simple for most cases. Refcounting will have to be adopted on the two sides: all functions returning a bridge pointer and all code obtaining such a pointer. This series has just an overview of some of those conversions, because for now the main goal is to agree on the API. Series layout: 1. Add the new API and refcounting: drm/bridge: add devm_drm_bridge_alloc() drm/bridge: add support for refcounting 2. get/put the reference in basic operations in the bridge core: drm/bridge: get/put the bridge reference in drm_bridge_add/remove() drm/bridge: get/put the bridge reference in drm_bridge_attach/detach() 3. as an example of changes for bridge consumers, get a reference for the bridge returned by drm_bridge_chain_get_first_bridge(), have it put by all callers (all users will be covered later on separately): drm/bridge: add a cleanup action for scope-based drm_bridge_put() invocation drm/bridge: get the bridge returned by drm_bridge_chain_get_first_bridge() drm/mxsfb: put the bridge returned by drm_bridge_chain_get_first_bridge() drm/atomic-helper: put the bridge returned by drm_bridge_chain_get_first_bridge() drm/probe-helper: put the bridge returned by drm_bridge_chain_get_first_bridge() 4. convert a few bridge drivers (bridge providers) to the new API: drm/bridge: ti-sn65dsi83: use dynamic lifetime management drm/bridge: samsung-dsim: use dynamic lifetime management This work was formerly a part of my v6 DRM bridge hotplug series[0], now split as a standalone series with many improvements, hence the "v7" version number. [0] https://lore.kernel.org/dri-devel/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/ Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com> --- Luca Ceresoli (11): drm/bridge: add devm_drm_bridge_alloc() drm/bridge: add support for refcounting drm/bridge: get/put the bridge reference in drm_bridge_add/remove() drm/bridge: get/put the bridge reference in drm_bridge_attach/detach() drm/bridge: add a cleanup action for scope-based drm_bridge_put() invocation drm/bridge: get the bridge returned by drm_bridge_chain_get_first_bridge() drm/mxsfb: put the bridge returned by drm_bridge_chain_get_first_bridge() drm/atomic-helper: put the bridge returned by drm_bridge_chain_get_first_bridge() drm/probe-helper: put the bridge returned by drm_bridge_chain_get_first_bridge() drm/bridge: ti-sn65dsi83: use dynamic lifetime management drm/bridge: samsung-dsim: use dynamic lifetime management drivers/gpu/drm/bridge/samsung-dsim.c | 7 +- drivers/gpu/drm/bridge/ti-sn65dsi83.c | 7 +- drivers/gpu/drm/drm_atomic_helper.c | 5 ++ drivers/gpu/drm/drm_bridge.c | 74 +++++++++++++++++++-- drivers/gpu/drm/drm_probe_helper.c | 1 + drivers/gpu/drm/mxsfb/lcdif_kms.c | 3 +- include/drm/drm_bridge.h | 119 +++++++++++++++++++++++++++++++++- 7 files changed, 201 insertions(+), 15 deletions(-) --- base-commit: 9e6d91c60b0d64a4f945663993b3bbf4f3fb7392 change-id: 20250314-drm-bridge-refcount-58d9503503f6 Best regards,