Hi Maxime, On Mon Dec 15, 2025 at 11:35 AM CET, Maxime Ripard wrote: [...] >> > Additionally, as a matter of fact there are currently drivers storing >> > bridge pointers. The next_bridge is the most common case. Code using >> > drm_bridge_connector_init() for example can store up to eight of them, but >> > individual drivers are the hardest to hunt for. >> > >> > I can see these (potential) tools to handle this (not mutually exclusive): >> > >> > 1. remove drm_bridge pointers pointing to other bridges >> > 2. check whether a bridge (say B) still exists before any dereference >> > to B->another_bridge: that's drm_bridge_enter/exit() >> > 3. let owners of bridge pointers be notified when a bridge is unplugged, >> > so they can actively put their reference and clear their pointer >> > >> > For item 1, I think the drm_of_bridge_attach() idea quoted above would >> > work, at least for the simple cases where bridge drivers use the >> > next_bridge only for attach. A next_bridge pointer in struct drm_bridge is >> > not even needed in that case, the pointer would be computed from OF when >> > needed and not stored. I can do an experiment and send a first series, do >> > you think it would be useful? >> >> I had a look and, while the implementation should be simple, only a few >> drivers could benefit right now. The majority fall into one of these >> categories: >> >> * drivers using drm_of_find_panel_or_bridge() or *_of_get_bridge() >> (maybe 60-80% of all drivers, those will have to wait for the panel >> improvements) >> * drivers using the next_bridge pointer for more than just attach >> * drivers doing more complicated stuff >> >> I think your "put next_bridge in __drm_bridge_free" idea would fit well the >> 2nd category and perhaps also the 1st one. For the 3rd category we'd need >> something different, e.g. a per-driver .destroy callback. > > Yep, that's fine. We should optimize for the common case, with an escape > hatch. That's exactly what we are talking about here.
Not sure why, but it's taking a while before I grasp your ideas about this series and meld them with mine. I hopefully got a clear POV now, so based on it my plan is to rework this series to: * keep drm_of_find_bridge() but renamed to of_drm_get_bridge(), and keep patches 1-5 (with the changes suggested by you and Louis, nothing big and all already sent in v2) * not add devm_drm_of_find_bridge() * add next_bridge pointer to struct drm_bridge and call drm_bridge_put(bridge->next_bridge) in __drm_bridge_free, document it * convert patches 7-26 to use bridge->next_bridge where applicable, or to do something different when needed * maybe remove part of patches 7-26 just to reduce spam and rework effort in case of further iterations, to send them separately once the approach is accepted Does it look OK? Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
