Messages in this thread | | | From | "Moffett, Kyle D" <> | Date | Thu, 22 Dec 2011 11:55:56 -0600 | Subject | Re: Driver core support for early platform devices |
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On Dec 22, 2011, at 12:45, Greg KH wrote: > On Thu, Dec 22, 2011 at 11:15:06AM -0600, Moffett, Kyle D wrote: >> Hi, >> >> I'm tinkering with some improvements to the way that OpenPIC/MPIC are >> detected and loaded on PowerPC platforms, and it seems like I am trying >> to use the driver model before it is fully initialized. >> >> In particular, it seems like it should be possible to simply declare an >> OpenPIC in the device-tree and have it automatically bound to a platform >> driver declaring the right OpenFirmware match strings. >> >> Unfortunately, it needs to be bound by init_IRQ() time, while the driver >> model does not get initialized until much later (after the scheduler is >> up and running). >> >> As far as I can tell, there seem to be 2 possible approaches to making >> that possible: >> >> (1) Split the driver-model initialization into "early" and "late" phases >> so that drivers can be registered and devices probed very early on >> and then replay the necessary scheduler-dependent things after the >> system is mostly started up (IE: devtmpfs, etc). > > We already have that today with the "early_platform*" functions, right? > Will those work for you, or do you need this for a bus you are creating > and not using the platform bus?
Well, I can't figure out how "early_platform" is actually supposed to integrate with the platform bus itself. It seems designed mostly for drivers like "earlyprintk" et. al. for which loading is controlled by a kernel parameter.
Specifically, I don't see any "early_platform" logic to match devices in the OF device-tree based on the driver "of_match" parameters, just based on text strings in early_param().
Furthermore, if I register an "early_platform" device, it seems to get unregistered when the normal driver model is brought up, instead of being sucked in and promoted to a normal platform_device. That code is pretty poorly documented and only used in a couple places right now, though, so it's possible I am misreading it.
Cheers, Kyle Moffett
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