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

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Date:	Thu, 4 Jun 2009 00:17:40 -0400
From:	Andres Salomon <dilinger@...labora.co.uk>
To:	Paul Fox <pgf@...top.org>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	dsaxena@...top.org
Subject: Re: [PATCH] forced recalibration for the OLPC hgpk touchpad

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?
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