linux-kernel - Re: [PATCH v1 5/5] driver-core: add driver asynchronous probe support

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Message-ID: <20140930071555.GB14081@wotan.suse.de>
Date:	Tue, 30 Sep 2014 09:15:55 +0200
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	gregkh@...uxfoundation.org, tiwai@...e.de, tj@...nel.org,
	arjan@...ux.intel.com, teg@...m.no, rmilasan@...e.com,
	werner@...e.com, oleg@...hat.com, hare@...e.com, bpoirier@...e.de,
	santosh@...lsio.com, pmladek@...e.cz, dbueso@...e.com,
	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>,
	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>,
	Praveen Krishnamoorthy <praveen.krishnamoorthy@...gotech.com>,
	Sreekanth Reddy <sreekanth.reddy@...gotech.com>,
	Abhijit Mahajan <abhijit.mahajan@...gotech.com>,
	Casey Leedom <leedom@...lsio.com>,
	Hariprasad S <hariprasad@...lsio.com>,
	MPT-FusionLinux.pdl@...gotech.com, linux-scsi@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH v1 5/5] driver-core: add driver asynchronous probe
	support

On Sun, Sep 28, 2014 at 12:22:47PM -0700, Dmitry Torokhov wrote:
> Hi Luis,
> 
> On Fri, Sep 26, 2014 at 02:57:17PM -0700, Luis R. Rodriguez wrote:
> > +static bool drv_enable_async_probe(struct device_driver *drv,
> > +				   struct bus_type *bus)
> > +{
> > +	struct module *mod;
> > +
> > +	if (!drv->owner || drv->sync_probe)
> > +		return false;
> 
> This bit is one of the biggest issues I have with the patch set. Why async
> probing is limited to modules only?

Because Tejun wanted to address this separately, so its not that we will restrict
this but we should have non-module solution added as an evolution on top of this,
as a secondary step.

> I mentioned several times that we need
> async probing for built-in drivers and the way you are structuring the flags
> (async by default for modules, possibly opt-out of async for modules, forcibly
> sync for built-in) it is hard to extend the infrastructure for built-in case.

I confess I haven't tried enabling built-in as a secondary step but its just
due to lack of time right now but I don't think impossible and think actually
think it should be fairly trivial. Are there real blockers to do this that
you see as an evolutionary step?

> Also, as far as I can see, you are only considering the case where driver is
> being bound to already registered devices. If you have a module that creates a
> device for a driver that is already loaded and takes long time to probe you
> would still be probing synchronously even if driver/module requested async
> behavior.

Can you provide an example code path hit here? I'll certainly like to address
that as well.

  Luis
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