linux-kernel - Re: [PATCH v5 2/5] driver core: Functional dependencies tracking support

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Date:   Sun, 13 Nov 2016 17:58:46 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Mark Brown <broonie@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Grant Likely <grant.likely@...retlab.ca>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [PATCH v5 2/5] driver core: Functional dependencies tracking
 support

On Tue, Nov 08, 2016 at 09:58:24PM +0100, Luis R. Rodriguez wrote:
> On Tue, Nov 08, 2016 at 08:43:35PM +0100, Greg Kroah-Hartman wrote:
> > Yes, you can iterate a
> > lot of times, but that's fine, we have time at boot to do that (and
> > really, it is fast.)
> 
> Deferred probe is left for late_initcall() [1] -- this *assumes* that the
> driver/subsystem can be loaded so late, and as per Andrzej this solution
> isunacceptable/undesirable. So it would be unfair and incorrect to categorize
> all drivers in the same boat, in fact given this lone fact it may be
> worth revisiting the idea I mentioned about a capability aspect to support
> a late deferred probe later. We tend to assume its fine, however it does
> not seem to be the case.
> 
> [1] drivers/base/dd.c:late_initcall(deferred_probe_initcall);

Note that driver_deferred_probe_trigger() is called not only from this
late_initcall but also from driver_bound().  In other words, whenever
a driver binds successfully, deferred devices will reprobe, and devices
which had to defer will not necessarily have to wait until late_initcall
until they're reprobed.  The late_initcall is just a way to tell devices
"this is last call".

Thanks,

Lukas