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

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Message-ID: <20140728165920.GF21930@wotan.suse.de>
Date:	Mon, 28 Jul 2014 18:59:20 +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 06:52:48PM +0200, Luis R. Rodriguez wrote:
> 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).

But come to think of it that will work well for devices already plugged in
so indeed I think that driver_deferred_probe_add() needs a check added
for for if (!driver_deferred_probe_enable) then we have to
driver_deferred_probe_trigger(). The driver_deferred_probe_enable is set
to false upon init, but later on late init it gets set to true so with
that check we'd  only generate the trigger after late init call.

I can fold that in the v2.

  Luis
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