linux-kernel - Re: [markgross@...ngar.org: [RFC] wake up notifications and suspend blocking (aka more wakelock stuff)]

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Date:	Sat, 15 Oct 2011 08:47:32 +1100
From:	NeilBrown <neilb@...e.de>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	markgross@...gnar.org, <linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, <arve@...roid.com>,
	<amit.kucheria@...aro.org>, <farrowg@...ibm.com>,
	"Dmitry Fink (Palm GBU)" <Dmitry.Fink@...m.com>,
	<linux-pm@...ts.linux-foundation.org>, <khilman@...com>,
	Magnus Damm <damm@...nsource.se>, <mjg@...hat.com>,
	<peterz@...radead.org>
Subject: Re: [markgross@...ngar.org: [RFC] wake up notifications and suspend
 blocking (aka more wakelock stuff)]

On Thu, 13 Oct 2011 11:16:23 -0400 (EDT) Alan Stern
<stern@...land.harvard.edu> wrote:

> On Thu, 13 Oct 2011, NeilBrown wrote:
> 
> > Nope, but I'm keen for you to convince me.  Identify a wakeup event that
> > cannot be made visible to poll (or to user-space by some other
> > mechanism) before the wakeup_source needs to be deactivated.  Or if I've
> > misunderstood what sort of notification is problematic, help me understand.
> 
> Here's an example (just for kicks, not completely relevant to your
> discussion): A USB keyboard key release.  Unlike key presses, key
> releases need not generate input events.  If no processes are
> monitoring the raw keyboard event queue then the release is not visible
> to userspace at all, hence not visible before the wakeup_source needs
> to be deactivated.
> 
> Alan Stern

As you say, not completely relevant.

If a tree falls in a forest with no one to here, does it make a sound?

similarly if an event happens that no-one is looking for, is it visible?
It doesn't really matter.

So at most this is a case of "is not made visible" rather than "cannot be
made visible".

The key-release just needs to clear the "key is pressed" state so that
auto-repeat stops and if it was a modifier, the modification is discarded.
That is all trivially done in some kernel driver while the wakeup_source is
active.

Thanks,
NeilBrown

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