linux-kernel - Re: [PATCH] driver core: add wait event for deferred probe

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Date:	Thu, 14 Feb 2013 17:42:40 +0000
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Arnd Bergmann <arnd@...db.de>,
	Haojian Zhuang <haojian.zhuang@...aro.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	viro@...iv.linux.org.uk, rusty@...tcorp.com.au,
	hpa@...ux.intel.com, jim.cromie@...il.com,
	linux-kernel@...r.kernel.org,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	broonie@...nsource.wolfsonmicro.com,
	Patch Tracking <patches@...aro.org>
Subject: Re: [PATCH] driver core: add wait event for deferred probe

On Thu, 14 Feb 2013 15:57:18 +0000, Arnd Bergmann <arnd@...db.de> wrote:
> On Thursday 14 February 2013, Haojian Zhuang wrote:
> > If you can change it into code in below, it could work. Otherwise, it
> > always fails.
> >         driver_deferred_probe_enable = true;
> >         driver_deferred_probe_trigger();
> > +      deferred_probe_work_func(NULL);
> >         return 0;
> > 
> > Because deferred_probe_work_func() depends on that deferred_probe is added
> > into deferred_probe_active_list. If driver_deferred_probe_trigger() isn't called
> > first, the deferred uart probe can't be added into active list. So even you call
> > work_func at here, it doesn't help.
> > 
> 
> Would that not cause two instances of the work function to run at the same time?
> That sounds like a source for a lot of problems.

Yes. Even ignoring the problems with device drivers not handling
multithreaded probing well, the current deferred probe wouldn't handle
it well. I could make it support multithreading, but I don't see a whole
lot of value there.

g.

-- 
Grant Likely, B.Sc, P.Eng.
Secret Lab Technologies, Ltd.
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