On Wed, May 28, 2025 at 11:29:36AM +0200, Luca Ceresoli wrote: > This is the new API for allocating DRM bridges. > > Converting this driver is a bit complex because the drm_bridge funcs > pointer differs based on the bridge mode. So the current code does: > > * tc_probe() > * devm_kzalloc() private struct embedding drm_bridge > * call tc_probe_bridge_endpoint() which > * parses DT description into struct fields > * computes the mode > * calls different bridge init functions based on the mode > * each sets a different bridge.funcs pointer > > The new API expects the funcs pointer to be known at alloc time, which does > not fit in the current code structure. > > Solve this by splitting tc_probe_bridge_endpoint() in two functions: > > * tc_probe_get_mode(), computing the mode without needing the private > driver structure > * tc_probe_bridge_endpoint(), only initializing the endpoints > > So now the mode is known before allocation and so > is the funcs pointer, while all other operations are still happening after > allocation, directly into the private struct data, as they used to. > > The new code flow is: > > * tc_probe() > * tc_probe_get_mode() > * parses DT description > * computes and returns the mode > * based onf the mode, pick the funcs pointer > * devm_drm_bridfge_alloc(..., funcs) > * call tc_probe_bridge_endpoint() which > * calls different bridge init functions based on the mode > * these don't set the funcs pointer, it was done by _alloc > > This solution is chosen to minimize the changes in the driver logical code > flow. The drawback is we now iterate twice over the endpoints during probe. > > Signed-off-by: Luca Ceresoli <luca.ceres...@bootlin.com> > --- > devm_drm_bridge_alloc() [0] is the new API to allocate and initialize a DRM > bridge, and the only one supported from now on. It is the first milestone > towards removal of bridges from a still existing DRM pipeline without > use-after-free. > > The steps in the grand plan [1] are: > > 1. ➜ add refcounting to DRM bridges (struct drm_bridge) > 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) > > This series is part of step 1 of the grand plan. > > Current tasks in step 1 of the grand plan: > > A. ✔ add new alloc API and refcounting -> (now in drm-misc-next) > B. ➜ convert all bridge drivers to new API (this series) > C. … documentation, kunit tests (v1 under discussion) > D. after (B), add get/put to drm_bridge_add/remove() + attach/detech() > E. after (B), convert accessors; this is a large work and can be done > in chunks > F. debugfs improvements > > More info about this series in the v2 cover [2]. > > Luca > > [0] > https://gitlab.freedesktop.org/drm/misc/kernel/-/commit/0cc6aadd7fc1e629b715ea3d1ba537ef2da95eec > [1] > https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3...@bootlin.com/t/#u > [2] > https://lore.kernel.org/lkml/20250424-drm-bridge-convert-to-alloc-api-v2-0-8f91a404d...@bootlin.com/ > --- > Changes in v4: > - Removed patches already in drm-misc-next -> only 1 left > - Improve commit message of patch 1 > - Link to v3: > https://lore.kernel.org/all/20250509-drm-bridge-convert-to-alloc-api-v3-0-b8bc1f16d...@bootlin.com/ > > Changes in v3: > - Fixed issues reported for some patches > - Added review tags > - Removed patches that have been applied > - Added revert for the exynos patch, applied by mistake > - Update cover with grand plan info and trim some of it > - Updated bouncing e-mail address in Cc list > - Link to v2: > https://lore.kernel.org/lkml/20250424-drm-bridge-convert-to-alloc-api-v2-0-8f91a404d...@bootlin.com/ > > Changes in v2: > - Improved cover letter with link to commit adding devm_drm_bridge_alloc() > - add review tags > - fix bugs in zynqmp, vc4 patches > - fix patch 1 error code checking > - Link to v1: > https://lore.kernel.org/r/20250407-drm-bridge-convert-to-alloc-api-v1-0-42113ff8d...@bootlin.com > --- >
Reviewed-by: Dmitry Baryshkov <dmitry.barysh...@oss.qualcomm.com> -- With best wishes Dmitry
