linux-kernel - Re: [RFC PATCH v3] drivercore: Add driver probe deferral mechanism

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Message-ID: <87d3edllum.fsf@ti.com>
Date:	Mon, 03 Oct 2011 16:02:57 -0700
From:	Kevin Hilman <khilman@...com>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Greg Kroah-Hartman <greg@...ah.com>,
	Dilan Lee <dilee@...dia.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Manjunath GKondaiah <manjunath.gkondaiah@...aro.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC PATCH v3] drivercore: Add driver probe deferral mechanism

Grant Likely <grant.likely@...retlab.ca> writes:

> 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.

This is great work, thanks!

For the TODO list:

While the proposed patch should solve probe order dependencies, I don't
think it will solve the suspend/resume ordering dependencies, which are
typically the same.

Currenly suspend/resume order is based on the order devices are *added*
(device_add() -> device_pm_add() -> device added to dpm_list), so
unfortunately, deferring probe isn't going to affect suspend/resume
ordering.

Extending this to also address suspend/resume ordering by also changing
when the device is added to the dpm_list (or possibly creating another
list) should probably be explored as well.

Kevin
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