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

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Message-ID: <20110926141643.GK2946@opensource.wolfsonmicro.com>
Date:	Mon, 26 Sep 2011 15:16:43 +0100
From:	Mark Brown <broonie@...nsource.wolfsonmicro.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>,
	Manjunath GKondaiah <manjunath.gkondaiah@...aro.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC PATCH v3] drivercore: Add driver probe deferral mechanism

On Thu, Sep 22, 2011 at 12:51:23PM -0600, 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.

So, one issue I did think of the other day while putting some support in
the regulator core for using this: what happens with devices which can
optionally use a resource but don't rely on it?  One example here is
that a lot of the MMC drivers have an optional regulator to control some
of the supplies for the cards.  If the reglator isn't there it won't be
used but it's not a blocker for anything.  Devices doing this would need
some way to figure out if they should -EBUSY or fail otherwise.
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