linux-kernel - Re: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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Message-ID: <20100602202300.468b73fe@notabene.brown>
Date:	Wed, 2 Jun 2010 20:23:00 +1000
From:	Neil Brown <neilb@...e.de>
To:	Florian Mickler <florian@...kler.org>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul@...p1.linux-foundation.org" <Paul@...p1.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Bottomley <James.Bottomley@...e.de>
Subject: Re: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8] 
 Suspend block api (version 8)

On Wed, 2 Jun 2010 10:50:39 +0200
Florian Mickler <florian@...kler.org> wrote:

> On Wed, 2 Jun 2010 18:06:14 +1000
> Neil Brown <neilb@...e.de> wrote:
> 
> > I cannot imagine why it would take multiple seconds to scan a keypad.
> > Can you explain that?
> > 
> > Do you mean while keys are held pressed?  Maybe you don't get a wake-up event
> > on key-release?  In that case your user-space daemon could block suspend
> > while there are any pressed keys....  confused.
> 
> IIRC, the device sends interrupts only for first key-down and
> last key-up.
> To detect simultaneous key-presses you must actively scan it after the
> first key-down.

That makes sense - thanks.
Presumably the first key-press gets to user-space promptly, so the user-space
suspend daemon can be told not to suspend until the last key-up.

Thanks,
NeilBrown
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