linux-kernel - Re: Driver core support for early platform devices

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Date:	Thu, 22 Dec 2011 09:45:21 -0800
From:	Greg KH <gregkh@...e.de>
To:	"Moffett, Kyle D" <Kyle.D.Moffett@...ing.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: Driver core support for early platform devices

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?

If the later, why not just duplicate the logic of the early_platform*
code for your bus?  Will that work?

thanks,

greg k-h
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