linux-kernel - Re: [GIT PULL] On-demand device probing

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Date:	Mon, 26 Oct 2015 03:51:38 -0700
From:	Michael Turquette <mturquette@...libre.com>
To:	"Rafael J. Wysocki" <rafael@...nel.org>,
	"Mark Brown" <broonie@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Rob Herring" <robh+dt@...nel.org>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"Tim Bird" <tim.bird@...ymobile.com>,
	"frowand.list@...il.com" <frowand.list@...il.com>,
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Subject: Re: [GIT PULL] On-demand device probing

Quoting Rafael J. Wysocki (2015-10-25 06:54:39)
> On Sun, Oct 25, 2015 at 12:06 AM, Mark Brown <broonie@...nel.org> wrote:
> > On Sat, Oct 24, 2015 at 04:17:12PM +0200, Rafael J. Wysocki wrote:
> >
> >> Well, I'm not quite sure why exactly everyone is so focused on probing here.
> >
> > Probe deferral is really noisy even if it's working fine on a given
> > system so it's constantly being highlighted to people in a way that
> > other issues aren't if you're not directly having problems.
> >
> > There's also the understanding people had that the order things get
> > bound changes the ordering for some of the other cases (perhaps it's a
> > good idea to do that, it seems likely to be sensible?).
> 
> But it really doesn't do that.  Also making it do so doesn't help much
> in the cases where things can happen asynchronously (system
> suspend/resume, runtime PM).
> 
> If, instead, there was a way to specify a functional dependency at the
> device registration time, it might be used to change the order of
> everything relevant, including probe.  That should help to reduce the
> noise you're referring to.

Taking it a step further, if functional dependencies were understood at
link-time then we could optimize link order as well. There are probably
lots of optimizations if we only made the effort to understand these
dependencies earlier.

Constructing the device/resource dependency graph before the device ever
boots sounds interesting to me.

Regards,
Mike

> 
> If the dependency could only be discovered at the probe time, the
> order of things might be changed in response to letting the driver
> core know about it rather than "just in case", which should be more
> efficient.
> 
> Thanks,
> Rafael
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