Hi Maxime, On Fri, 25 Jul 2025 17:22:47 +0200 Maxime Ripard <mrip...@kernel.org> wrote:
... > > The question is: should a DSI host bridge driver: > > > > A) wait for a DSI device to .attach before drm_bridge_add()ing itself, > > or > > B) drm_bridge_add() itself unconditionally, and let the DSI device > > .attach whenever it happens? > > > > A) is what many drivers (IIRC the majority) does. It implies the card > > will not be populated until .attach, which in the hotplug case could > > happen very late > > > > B) is done by a few drivers and allows the card to appear in the > > hotplug case without the device, which is needed for hotplug. > > > > I had tried simply moving drm_bridge_add() from .attach to probe in > > the samsung-dsim driver in the pase but that would not work. Now I did > > yet another check at the code and I suspect it can be done with a small > > additional change, but cannot access the hardware to test it currently. > > > > Answering this last question might change and simplify the requirements > > discussed in the (very lengthy, sorry about that) discussion above. > > You're not going to like the answer too much, but I think that it is > that "nobody knows". > > The bad news is that I can't give you an answer, but the good one is > that it gives us some leeway. > > As I said in my previous mail, we should probably figure it out, > document it, and then make it work for your drivers. Once we have a > documentation we can point to, the rest will fall in line. Thanks for taking time to reply this! I just sent a patch to do the mentioned change in samsung-dsim [0] to start discussion on real code. I'd appreciate if you could prioritize that patch over all other patches I have sent. [0] https://lore.kernel.org/all/20250725-drm-bridge-samsung-dsim-add-in-probe-v1-1-b23d29c23...@bootlin.com/ Best regards, Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
