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SubjectRe: [PATCH] forced recalibration for the OLPC hgpk touchpad
On Wed, 03 Jun 2009 23:58:33 -0400
Paul Fox <pgf@laptop.org> wrote:

> dmitry wrote:
> > Hi Paul,
> >
> > On Tuesday 02 June 2009 12:47:59 pgf@laptop.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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