On Mon, 10 Feb 2025 at 14:31, Maxime Ripard <mripard@xxxxxxxxxx> wrote: > > On Fri, Feb 07, 2025 at 09:54:06PM +0200, Dmitry Baryshkov wrote: > > On Fri, Feb 07, 2025 at 12:47:51PM +0100, Maxime Ripard wrote: > > > Hi, > > > > > > On Thu, Feb 06, 2025 at 07:14:29PM +0100, Luca Ceresoli wrote: > > > > DRM bridges are currently considered as a fixed element of a DRM card, and > > > > thus their lifetime is assumed to extend for as long as the card > > > > exists. New use cases, such as hot-pluggable hardware with video bridges, > > > > require DRM bridges to be added and removed to a DRM card without tearing > > > > the card down. This is possible for connectors already (used by DP MST), so > > > > add this possibility to DRM bridges as well. > > > > > > > > Implementation is based on drm_connector_init() as far as it makes sense, > > > > and differs when it doesn't. A difference is that bridges are not exposed > > > > to userspace, hence struct drm_bridge does not embed a struct > > > > drm_mode_object which would provide the refcount. Instead we add to struct > > > > drm_bridge a refcount field (we don't need other struct drm_mode_object > > > > fields here) and instead of using the drm_mode_object_*() functions we > > > > reimplement from those functions the few lines that drm_bridge needs for > > > > refcounting. > > > > > > > > Also add a new devm_drm_bridge_alloc() macro to allocate a new refcounted > > > > bridge. > > > > > > > > Signed-off-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx> > > > > > > So, a couple of general comments: > > > > > > - I've said it a couple of times already, but I really think you're > > > making it harder than necessary for you here. This (and only this!) > > > should be the very first series you should be pushing. The rest can > > > only ever work if that work goes through, and it's already hard enough > > > as it is. So, split that patch into a series of its own, get that > > > merged, and then we will be able to deal with panels conversion and > > > whatever. That's even more true with panels since there's ongoing work > > > that will make it easier for you too. So the best thing here is > > > probably to wait. > > > > Luca and I had a quick chat on this during FOSDEM. I really think that > > panel (part of the) series can go in first as it fixes a very well known > > bug _and_ allows a pretty good cleanup to a whole set of drivers. > > I don't necessarily disagree on principle, but if you state that it can > get first, and fixes a known problem (which one?), then it should be a > separate, standalone, series. A problem of panel bridges having the wrong lifetime because of devm_ attachment to a wrong device and so either being kept for too long or being destroyed too early. > > Ever-expanding features are bad for both the reviewers and the > contributors, even more so when the discussion happens off-list. > > > With all those panel / bridge wrappers gone we should be able to see a > > clearer picture of what individual drivers are doing. In other words, > > which memory and which code actually hosts and uses internal > > 'next_bridge' reference. > > > > > - This patch really needs to be split into several patches, something > > > along the lines of: > > > > > > + Creating devm_drm_bridge_alloc() > > > + Adding refcounting > > > + Taking the references in all the needed places > > > + Converting a bunch of drivers > > > > The last two parts seem troublematic to me, but, I must admit, I didn't > > spend so much time reviewing all drm_bridge usage patterns. > > Why? the third one is already done by that patch, the fourth can > relatively easily be done using coccinelle. I have doubts about cocci. It doesn't have a way to know, what is the lifetime of the references to the reference-holding memory. Maybe I'm missing a point there. -- With best wishes Dmitry
