linux-kernel - Re: [PATCH 2/2] input: mt: Document the MT event slot protocol (rev2)

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Message-Id: <201005241021.02731.dmitry.torokhov@gmail.com>
Date:	Mon, 24 May 2010 10:21:02 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Ping Cheng <pinglinux@...il.com>
Cc:	Peter Hutterer <peter.hutterer@...-t.net>,
	Henrik Rydberg <rydberg@...omail.se>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mika Kuoppala <mika.kuoppala@...ia.com>,
	Benjamin Tissoires <tissoire@...a.fr>,
	Stephane Chatty <chatty@...c.fr>,
	Rafi Rubin <rafi@...s.upenn.edu>,
	Michael Poole <mdpoole@...ilus.org>
Subject: Re: [PATCH 2/2] input: mt: Document the MT event slot protocol (rev2)

On Monday 24 May 2010 10:06:15 am Ping Cheng wrote:
> On Mon, May 24, 2010 at 8:59 AM, Dmitry Torokhov
> 
> <dmitry.torokhov@...il.com> wrote:
> > On Sun, May 23, 2010 at 11:07:27PM -0700, Ping Cheng wrote:
> >> On Sun, May 23, 2010 at 9:58 PM, Peter Hutterer
> >> 
> >> <peter.hutterer@...-t.net> wrote:
> >> >> > And yes, you could add it once we find it's an issue, but by then
> >> >> > someone has already spent time to work around this. And when you
> >> >> > then start sending slot events all the time, you admit that
> >> >> > writing the workaround was just a time waster :)
> >> >> 
> >> >> Work around what, exactly?
> >> > 
> >> > I was referring to having a protocol where processes has to ignore
> >> > contacts already down until they've been there when a contact was
> >> > pressed (and your comment that if this becomes an issue it could be
> >> > added lateron). Now, the ignoring part needs to be written (this is
> >> > the "workaround" referred to above). if you're planning to add it
> >> > later, we need to cater for that part as well then, having two
> >> > implementations depending on the kernel versions.
> >> > 
> >> > but this is just for clarification, it's a moot point anyway given
> >> > that button events have the same behaviour.
> >> 
> >> This topic is outside of the _MT_ protocol discussion.
> >> 
> >> However, it is indeed an issue with all filtered input events, both
> >> for MT and regular ones.
> >> 
> >> I think we need to add an ioctl to enable user land driver/client to
> >> signal the kernel driver to send all events without filtering, just
> >> once. Hot-plugged devices and X driver starts after user has contacted
> >> with the device are two examples that the client would miss filtered
> >> events.
> >> 
> >> Dmitry, do you think it is a valid suggestion?
> > 
> > What about using EVIOCGKEY/EVIOCGSW/EVIOCGABS?
> 
> Those EVIOCs only give us the static values (max/min/supported keys,
> etc.).  We need their dynamic input data here, the actual x, y,
> button, pressure, etc. Am I missing something about those EVIOs?
> 

Yes you are ;) Supported events are reported via EVIOCGBIT, EVIOCGKEY and
EVIOCGSW will return current state of keys/switches. As far as EVIOCGABS
goes, it also returns, besides min/max/etc, last reported _values_ of the
ABS_* events.

-- 
Dmitry
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