linux-kernel - Re: [RESEND] [PATCH] Input: add appleir USB driver

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Date:	Tue, 5 Oct 2010 08:55:52 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	Bastien Nocera <hadess@...ess.net>,
	linux-input <linux-input@...r.kernel.org>,
	Jiri Kosina <jkosina@...e.cz>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND] [PATCH] Input: add appleir USB driver

On Tue, Oct 05, 2010 at 08:18:35AM +0200, Oliver Neukum wrote:
> Am Dienstag, 5. Oktober 2010, 08:08:22 schrieb Dmitry Torokhov:
> > > But what about the next opener? He'll get a completely spurious
> > > key release event, as the next key is pressed.
> > 
> > How does the opening of a device handle relate to a device state?
> 
> It doesn't.
> 
> > Userspace should expect to see releases without presses (in case they
> > weren't the first client that opened the device).
> 
> Yes, but based on sane timing. From the time stamps user space
> would conclude that the key had been pressed at an unknown time
> before open and released at the time the event indicates. Possibly
> it would compute that the key had been held for at least hours.
> 

I do not understand. If a client never seen the "press" event and only
saw "release" event it can't make any assumptions about timing. Press
could be a millisecond ago or an hour ago, it just does not know. And
such scenario can easily happen if the client is second to open the
device.

I think the only sane behavior for clients is to ignore release events
for keys that they did not see "down" event for.

- 
Dmitry
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