linux-kernel - Re: [PATCH 0/2] input: mt: Add helper function to send end events

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Date:	Wed, 1 Jan 2014 11:18:39 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Henrik Rydberg <rydberg@...omail.se>
Cc:	"Felipe F. Tonello" <eu@...ipetonello.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] input: mt: Add helper function to send end events

On Wed, Jan 01, 2014 at 05:19:10PM +0100, Henrik Rydberg wrote:
> Hi Dmitry,
> 
> >> What problematic scenario is this supposed to solve?
> >>
> >> The 'release on suspend' is only an approximation to the 'close
> >> laptop' scenario, it is certainly not correct in the coffee table
> >> case,
> > 
> > Why would it not be correct for coffee table? Do we expect the touches
> > to remain valid while the device is asleep?
> 
> In some scenarios with placed objects (like a cup or a marker), that would be
> the case, yes.
> 
> >> for instance. Instead of
> >> hardcoding this in the kernel, userland can easily detect long intervals
> >> directly using the event time.
> > 
> > But with slots it is not only problem with old events being sent out
> > later, it is that we have mix of old (pre-sleep) and new state.
> 
> The new state is not really a problem, it will look exactly the same regardless
> of how 'old' releases are handled.
> 
> > We do that for keys (release them when we transition to system sleep)
> > and I think it might be worthwhile to do the same for touch data.
> 
> I agree that keyboard applications seldom look at time intervals and hence are
> well helped by such a strategy, even though it is not strictly 'correct'.
> However, touch interfaces are quite dependent on time intervals, and it
> therefore makes a lot of sense to resolve touch timeouts directly in the
> application. It also puts less restrictions on what can be done.
> 
> Regarding notifications in general, perhaps it would be interesting to be able
> to send a notification event via the input interface when a device comes back
> from sleep. It could help resolve other complex issues, if there were any.
> 

OK, fair enough. If there is a demand we could send SYN_SYSTEM_RESUME
event though the interfaces to allow clients "flush" the state or
otherwise decide if new touch data is actually old touches that were
there pre-suspend.

Felipe, will that help in your case?

Thanks.

-- 
Dmitry
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