On 02/23/2017 10:23 PM, Heiner Kallweit wrote: > Am 23.02.2017 um 22:08 schrieb Pavel Machek: >> On Wed 2017-02-22 21:35:52, Heiner Kallweit wrote: >>> When registering a LED device we have the option to set a default trigger. >>> Depending on load order of drivers this trigger may not be available yet. >>> (affected LED device in my case: a DT-configured GPIO LED) >>> So far if the default trigger can't be found this error is silently >>> ignored. >>> >>> Let's change this to return EPROBE_DEFER if the default trigger can't be >>> found. This gives the system the chance to probe the LED device later >>> once the trigger is available. >> >> I see a lot of EPROBE_DEFERs on N900, and it is quite nasty, as it >> spams a log a lot. >> > Usually error messages are printed only if there is an error and it is not > EPROBE_DEFER. However indeed there still may be several drivers not > taking into account that a subsystem they depend on may return > EPROBE_DEFER and this should not be treated as "hard error". > >> Rather then re-trying LED registration few times, could we make sure >> leds are always registered after triggers or something like that? >> > I'm afraid if guaranteeing a particular order would be possible w/o > significant effort then the whole deferred probing concept wouldn't exist. > > I could imagine that we can try reordering definitions in the DTS to > ensure a certain load order. But this might be somewhat fragile. > So using the existing concept of deferred probing seems to me to be > the cleaner solution. We could go for a solution similar to v4l2-async.c mechanism which allows for deferring video pipeline linking until all video pipeline entities are probed, but in the LED subsystem case I think it would be an overengineering. V4L2 media device has to wait for completion of probing of several v4l2 drivers, whereas here we've got to wait for a single driver. EPROBE_DEFER seems to fit for that ideally. -- Best regards, Jacek Anaszewski
