Message-ID: <CAAObsKAFJ+OKiLR2aMOjf15bd7k89EKsKLpd3ubsPMKeGLkRZw@mail.gmail.com>
Date:	Mon, 26 Oct 2015 13:55:29 +0100
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Michael Turquette <mturquette@...libre.com>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Mark Brown <broonie@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
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Subject: Re: [GIT PULL] On-demand device probing

On 26 October 2015 at 11:51, Michael Turquette <mturquette@...libre.com> wrote:
> 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.

Alexander Holler has been looking at that for some time already.

Regards,

Tomeu

> 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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