On Wed, Nov 05, 2014 at 05:00:47PM +0100, Andrzej Hajda wrote: > On 11/05/2014 03:04 PM, Thierry Reding wrote: > > On Wed, Nov 05, 2014 at 01:36:24PM +0100, Andrzej Hajda wrote: > >> On 11/04/2014 05:29 PM, Thierry Reding wrote: > >>> From: Thierry Reding <treding@xxxxxxxxxx> > >>> > >>> Add a generic implementation of an object registry. This targets drivers > >>> and subsystems that provide auxiliary objects that other drivers need to > >>> look up. The goal is to put the difficult parts (keep object references, > >>> module usage count, ...) into core code so that individual subsystems do > >>> not have to deal with them. > >>> > >>> The intention is for subsystems to instantiate a struct registry and use > >>> a struct registry_record embedded into a subsystem-specific structure to > >>> provide a subsystem-specific API around that. > >> > >> > >> As I understand you want to use this registry for panels and bridges. > >> Could you explain the idea and describe example scenario when these > >> refcountings are useful. I guess it should be when panel attached to > >> drmdrv want to disappear. > > > > Correct. When a panel driver is unloaded it frees memory associated with > > the panel. The goal of this registry is for the panel object to stay > > around until all references are gone. > > > >> Real lifetime of panel is limited by probe/remove callbacks of panel > >> driver, do you want to prolong it behind these limits? > > > > Yes. > > > >> Do you want to have zombie panels, without hardware they abstract? For > >> what purpose? > > > > So that display drivers don't try to access objects that have been > > freed. > > Why do not just release panel references from drm_dev, I have > successfully implemented dsi panels this way, thanks to dsi bus specific > attach/detach callbacks and drm hotplug mechansim. Like you say yourself, that's something that work only for DSI. Any other type of panel can't do this. > My point is we do not need to make the whole tricky double refcounting, There's no double refcounting. We have no refcounting at all at the moment. > with total redesign of panels, revoke, zombies, etc.... It is enough to It's not a total redesign. It just makes it more mature and implements features that I think are useful (and needed) but that were left out for the sake of simplicity. Now it turns out that this is actually quite fragile and easy to get wrong. > have just hot plug/unplug callbacks. This is why I have proposed few > months ago interface_tracker framework. It can add hot(un)plug > capability in a generic way to any framework. That's something that this object registry could easily implement as well. But instead of passing around void * and type IDs as in the interface tracker it could deal with real objects for proper type- safety. Thierry
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