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

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Message-ID: <19417.1244087913@foxharp.boston.ma.us>
Date:	Wed, 03 Jun 2009 23:58:33 -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,
	dilinger@...top.org, dsaxena@...top.org
Subject: Re: [PATCH] forced recalibration for the OLPC hgpk touchpad 

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.)

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