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

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Date:   Tue, 8 Nov 2016 20:43:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     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>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Grant Likely <grant.likely@...retlab.ca>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Andrzej Hajda <a.hajda@...sung.com>
Subject: Re: [PATCH v5 2/5] driver core: Functional dependencies tracking
 support

On Tue, Nov 08, 2016 at 08:21:04PM +0100, Luis R. Rodriguez wrote:
> On Tue, Nov 08, 2016 at 07:45:41AM +0100, Greg Kroah-Hartman wrote:
> > On Mon, Nov 07, 2016 at 10:22:50PM +0100, Luis R. Rodriguez wrote:
> > > We have no explicit semantics to check if a driver / subsystem
> > > supports deferred probe.
> > 
> > Why would we need such a thing?
> 
> It depends on the impact of a driver/subsystem not properly supporting
> deffered probe, if this is no-op then such a need is not critical but
> would be good to proactively inform developers / users so they avoid 
> its use, if this will cause issues its perhaps best to make this a
> no-op through a check. AFAICT reviewing implications of not supporting
> deferred probe on drivers/subsytsems for this framework is not clearly
> spelled out, if we start considering re-using this framework for probe
> ordering I'd hate to see issues come up without this corner case being
> concretely considered.

It should not matter to the driver core if a subsystem, or a driver,
supports or does not support deferred probe.  It's a quick and simple
solution to a complex problem that works well.  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.)

> Furthermore -- how does this framework compare to Andrzej's resource tracking
> solution? I confess I have not had a chance yet to review yet but in light of
> this question it would be good to know if Andrzej's framework also requires
> deferred probe as similar concerns would exist there as well.

I have no idea what "framework" you are talking about here, do you have
a pointer to patches?

thanks,

greg k-h