linux-kernel - Re: [PATCH] forced recalibration for the OLPC hgpk touchpad

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Date:	Wed, 17 Jun 2009 16:16:11 -0400
From:	Paul Fox <pgf@...top.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	dsaxena@...top.org, Andres Salomon <dilinger@...labora.co.uk>
Subject: Re: [PATCH] forced recalibration for the OLPC hgpk touchpad 

hi dmitry --

have you had a chance to think any more about this?  i'm open to
suggestions on implementation detail, but i think that a full
reset of the device won't really work, because of the time it
adds to the recalibration.

paul

andres wrote:
 > On Wed, 03 Jun 2009 23:58:33 -0400
 > Paul Fox <pgf@...top.org> wrote:
 > 
 > > dmitry wrote:
 > >  > Hi Paul,
 > >  > 
 > >  > On Tuesday 02 June 2009 12:47:59 pgf@...top.org wrote:
 > >  > > The OLPC XO laptop incorporates a combination touchpad/tablet
 > >  > > device which unfortunately requires frequent recalibration.  The
 > >  > > driver will force this automatically when various suspicious
 > >  > > behaviors are observed, and the user can recalibrate manually
 > >  > > (with a special keyboard sequence).  There's currently no way,
 > >  > > however, for an external program to cause recalibration.
 > >  > >
 > >  > > This patch creates a new node in /sys which, when written with
 > >  > > '1', will force a touchpad recalibration.  No other writes (or
 > >  > > reads) of this node are supported.
 > >  > >
 > >  > 
 > >  > 
 > >  > Instead of creating a new sysfs attribute maybe we should make
 > >  > the touchpad recalibrate upon resume (reconnect)? Userspace can
 > >  > already request reconnect via sysfs.
 > > 
 > > dmitry -- thanks for the suggestion.
 > > 
 > > i took a look, and tried it.  the problem is that doing a full
 > > reset of the touchpad takes quite a long time -- 1.1 or 1.2
 > > seconds.  recalibration deprives the user of their touchpad for
 > > long enough as it is -- i don't think we can afford that time.
 > > (remember that this is a workaround for bad hardware -- the XO
 > > no longer uses this touchpad at least partly due to this very
 > > issue, but there are enough in use that we're still trying to
 > > improve things.)
 > > 
 > 
 > I do like the idea of having a sysfs trigger for recalibrations.  We've
 > never been successful in having the kernel driver handle recalibrations
 > seamlessly.  Perhaps touchpad hardware screwups would be easier to
 > detect in userspace, given a daemon that can keep a history of the last
 > N touchpad coordinates?

=---------------------
 paul fox, pgf@...top.org
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