linux-kernel - Re: [PATCH] drivercore: Add driver probe deferral mechanism

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Date:	Thu, 8 Mar 2012 12:22:18 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	linux-kernel@...r.kernel.org, Tony Lindgren <tony@...mide.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Arnd Bergmann <arnd@...db.de>, Dilan Lee <dilee@...dia.com>,
	Manjunath GKondaiah <manjunath.gkondaiah@...aro.org>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH] drivercore: Add driver probe deferral mechanism

On Mon, Mar 05, 2012 at 08:47:41AM -0700, Grant Likely wrote:
> Allow drivers to report at probe time that they cannot get all the resources
> required by the device, and should be retried at a later time.
> 
> This should completely solve the problem of getting devices
> initialized in the right order.  Right now this is mostly handled by
> mucking about with initcall ordering which is a complete hack, and
> doesn't even remotely handle the case where device drivers are in
> modules.  This approach completely sidesteps the issues by allowing
> driver registration to occur in any order, and any driver can request
> to be retried after a few more other drivers get probed.
> 
> v4: - Integrate Manjunath's addition of a separate workqueue
>     - Change -EAGAIN to -EPROBE_DEFER for drivers to trigger deferral
>     - Update comment blocks to reflect how the code really works
> v3: - Hold off workqueue scheduling until late_initcall so that the bulk
>       of driver probes are complete before we start retrying deferred devices.
>     - Tested with simple use cases.  Still needs more testing though.
>       Using it to get rid of the gpio early_initcall madness, or to replace
>       the ASoC internal probe deferral code would be ideal.
> v2: - added locking so it should no longer be utterly broken in that regard
>     - remove device from deferred list at device_del time.
>     - Still completely untested with any real use case, but has been
>       boot tested.

Now applied, thanks for pushing this and seeing it through.

greg k-h
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