Re: [PATCH v5 2/5] driver core: Functional dependencies tracking support - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: Lukas Wunner <lukas@wunner.de>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Linux PM list <linux-pm@vger.kernel.org>,
	Alan Stern <stern@rowland.harvard.edu>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Tomeu Vizoso <tomeu.vizoso@collabora.com>,
	Mark Brown <broonie@kernel.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Kevin Hilman <khilman@kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Grant Likely <grant.likely@secretlab.ca>,
	Mauro Carvalho Chehab <mchehab@osg.samsung.com>,
	Andrzej Hajda <a.hajda@samsung.com>
Subject: Re: [PATCH v5 2/5] driver core: Functional dependencies tracking support
Date: Tue, 8 Nov 2016 20:43:35 +0100	[thread overview]
Message-ID: <20161108194335.GA22680@kroah.com> (raw)
In-Reply-To: <20161108192103.GN1764@wotan.suse.de>

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