linux-kernel - Re: [PATCH 1/3] driver core: enable drivers to use deferred probe from init

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Date:	Mon, 28 Jul 2014 18:52:48 +0200
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Yuval Mintz <Yuval.Mintz@...gic.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Joseph Salisbury <joseph.salisbury@...onical.com>,
	Kay Sievers <kay@...y.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Tim Gardner <tim.gardner@...onical.com>,
	Pierre Fersing <pierre-fersing@...rref.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Benjamin Poirier <bpoirier@...e.de>,
	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	Hariprasad S <hariprasad@...lsio.com>,
	Santosh Rastapur <santosh@...lsio.com>,
	"MPT-FusionLinux.pdl@...gotech.com" 
	<MPT-FusionLinux.pdl@...gotech.com>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/3] driver core: enable drivers to use deferred probe
	from init

On Mon, Jul 28, 2014 at 03:46:32PM +0000, Yuval Mintz wrote:
> > Subject: Re: [PATCH 1/3] driver core: enable drivers to use deferred probe from
> > init
> > 
> > On Mon, Jul 28, 2014 at 03:12:11PM +0000, Yuval Mintz wrote:
> > > Perhaps this is a silly question, but what guarantees that the
> > > deferred probe list will actually be triggered, e.g., in case the
> > > delayed device is the last device in the system?
> > 
> > The dev->init_delayed_probe is used to ensure that we'd add the device to the
> > deferred probe list once making this a per device thing if the driver has the field
> > delay_probe set to true. This technically also allows this to be a per device thing
> > so with some more work we could enable drivers to only enable this for specific
> > devices but at this point this did not seem required.
> 
> Sorry for not being clear, but I didn't meant 'what guarantees that the device
> will be added to the deferred probe', but rather what guarantees that the
> deferred workqueue will be scheduled.
> 
> To the best of my knowledge the deferring mechanism works only if one device
> is dependent upon another, e.g., for Multi-function devices where one device
> probe is dependent upon the others - which are soon-to-be probed.

The workqueue will be kicked when driver_deferred_probe_trigger() gets
poked, we do that in the late_initcall(deferred_probe_initcall), it
also gets flushed there with a flush_workqueue(deferred_wq).

  Luis
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