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

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Message-Id: <201107051805.00696.arnd@arndb.de>
Date:	Tue, 5 Jul 2011 18:05:00 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Greg KH <gregkh@...e.de>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] drivercore: Add driver probe deferral mechanism

On Tuesday 05 July 2011, Greg KH wrote:
> > * go through all initcalls, record any devices that are not yet ready
> > * retry all devices on the list as long as at least one of them has
> >   succeeded.
> > * when a new device gets matched from a module load, do that loop again
> 
> You don't know when init calls are finished, or if a module is loaded,
> the driver core isn't that smart at all.

We know when most initcalls are finished (at late_initcall time), and
after that we don't need to know when a module gets loaded, only 
when a device gets matched, and that's something we do know and
that Grant's patch uses already.

> > late_initcall(retry_devices);
> 
> I wonder if doing this all from a workqueue in the first place is going
> to cause problems as probe isn't normally done this way at all.

True. It will definitely cause problems for any driver that calls
flush_work() in its probe function. We would need a private
singlethread_workqueue to avoid that.

	Arnd
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