linux-kernel - Re: Async suspend-resume patch w/ completions (was: Re: Async suspend-resume patch w/ rwsems)

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Message-ID: <alpine.LFD.2.00.0912191557320.3712@localhost.localdomain>
Date:	Sat, 19 Dec 2009 16:09:07 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Zhang Rui <rui.zhang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: Async suspend-resume patch w/ completions (was: Re: Async
 suspend-resume patch w/ rwsems)

On Sun, 20 Dec 2009, Rafael J. Wysocki wrote:
> > 
> > Why would it be?
> 
> The embedded controller may depend on it.

Again, I say "why?"

Anything can be true. That doesn't _make_ everything true. There's no real 
reason why PnP/ACPI suspend/resume should really care.

We can try it. Not for 2.6.33, but by the 34 merge window maybe we'll have 
a patch-series that is ready to be tested, and that aggressively tries to 
do the devices that matter asynchronously.

So instead of you trying to make up some idiotic cross-device worries, 
just see if those worries have any actual background in reality. So far I 
haven't actually heard anything but "in theory, anything is possible", 
which is such a truism that it's not even worth voicing.

That said, I still get the feeling that we'd be even better off simply 
trying to avoid the whole keyboard reset entirely. Apparently we do it for 
a few HP laptops. It's entirely possible that we'd be better off simply 
not _doing_ the slow thing in the first place.

For example, we may be _much_ better off doing that whole keyboard reset 
at resume time than at suspend time. That's what we do when we probe 
things on initialization - and the resume-time keyboard code is actually 
already asynchronous, it does that atkbd_reconnect asynchronously by 
queuing it as an event.

So again, all these problems may not at all be fundamnetal problems: the 
keyboard driver does certain things, but there is no guarantee that it 
_needs_ to do those things. Turning the driver async may be totally the 
wrong thing to do, when we could potentially fix latency problems at the 
driver level instead.

			Linus
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