linux-kernel - Re: [PATCH] Input: twl4030 power button: don't lose presses on resume

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Date:	Thu, 26 Apr 2012 17:14:16 +1000
From:	NeilBrown <neilb@...e.de>
To:	NeilBrown <neilb@...e.de>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: twl4030 power button: don't lose presses on
 resume

On Wed, 25 Apr 2012 15:26:03 +1000 NeilBrown <neilb@...e.de> wrote:

> On Tue, 24 Apr 2012 22:09:19 -0700 Dmitry Torokhov
> <dmitry.torokhov@...il.com> wrote:
> 
> > Hi Neil,
> > 
> > On Wed, Apr 25, 2012 at 12:21:39PM +1000, NeilBrown wrote:
> > > 
> > > If we press and release the power button before the press interrupt is
> > > handled - as can happen on resume - we lose the press event so the
> > > release event is ignored and we don't know what happened to cause the
> > > wakeup.
> > 
> > What kind of latency do you observe?
> 
> When I have debugging enabled, hundreds of milliseconds.
> 
> When I don't have debugging enabled ... it doesn't tell me, but I'm fairly
> sure it is several tens of milliseconds and the button press can be quicker
> than that.
> 
> If it will help I can try to instrument the driver and get some timings.

I added a bit of tracing.

It looks like a fast button press typically shows about 120ms between 'press'
and 'release', though I have seen as low as 70ms.
When I don't have PM_DEBUG debugging on, the 'press' interrupt gets handled
in about 14ms.
So it seems likely that the times that I suffered from the problem and so
wrote the patch, I had PM_DEBUG enabled which slows resume down quite a lot.

So I cannot make a strong case for these patches.  However I think it is
safer to have them than not :-)

Thanks,
NeilBrown

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