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

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Date:   Thu, 10 Nov 2016 01:43:38 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Lukas Wunner <lukas@...ner.de>,
        "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>
Subject: Re: [PATCH v5 2/5] driver core: Functional dependencies tracking support

On Mon, Nov 7, 2016 at 10:22 PM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
> On Thu, Oct 27, 2016 at 05:25:51PM +0200, Greg Kroah-Hartman wrote:
>> On Wed, Oct 26, 2016 at 01:19:02PM +0200, Lukas Wunner wrote:
>> > Hi Rafael,
>> >
>> > sorry for not responding to v5 of your series earlier, just sending
>> > this out now in the hope that it reaches you before your travels.
>> >
>> > On Mon, Oct 10, 2016 at 02:51:04PM +0200, Rafael J. Wysocki wrote:
>> > > - Modify device_links_check_suppliers(), device_links_driver_bound(),
>> > >   device_links_no_driver(), device_links_driver_cleanup(), device_links_busy(),
>> > >   and device_links_unbind_consumers() to walk link lists under device_links_lock
>> > >   (to make the new "driver presence tracking" mechanism work reliably).
>> >
>> > This change might increase boot time if drivers return -EPROBE_DEFER.
>>
>> "might"?  Please verify this before guessing....
>>
>> And don't make this more complex than needed before actually determining
>> a real issue.
>
> As clarified by Rafael at Plumbers, this functional dependencies
> framework assumes your driver / subsystem supports deferred probe,

It isn't particularly clear what you mean by "support" here.

I guess that you mean that it will allow the ->probe callback to be
invoked for multiple times for the same device/driver combination
without issues.  If that's the case, the way the new code uses
-EPROBE_DEFER doesn't interfere with this, because it will not invoke
the ->probe callbacks for consumers at all until their (required)
suppliers are ready.

> if it does not support its not clear what will happen....

I don't see any problems here, but if you see any, please just say
what they are.

> We have no explicit semantics to check if a driver / subsystem
> supports deferred probe.

That's correct, but then do we need it?

Thanks,
Rafael