linux-kernel - Re: [PATCH 1/4] Adding documention

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Message-ID: <alpine.LNX.2.00.1008301525240.1019@pobox.suse.cz>
Date:	Mon, 30 Aug 2010 15:25:41 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Rafi Rubin <rafi@...s.upenn.edu>
Cc:	Henrik Rydberg <rydberg@...omail.se>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, dmitry.torokhov@...il.com,
	chatty@...c.fr, micki@...rig.com
Subject: Re: [PATCH 1/4] Adding documention

On Sun, 29 Aug 2010, Rafi Rubin wrote:

> >> +----------
> >> +
> >> +Note: values set at load time are global and will apply to all applicable
> >> +devices.  Adjusting parameters with sysfs will override the load time values,
> >> +but only for that one device.
> >> +
> >> +The following parameters are used to configure filters to reduce noise:
> >> +
> >> +activate_slack		number of fingers to ignore before processing events
> >> +
> >> +activation_height	size threshold to activate immediately
> >> +activation_width
> >> +
> >> +min_height		size threshold bellow which fingers are ignored
> >> +min_width		both to decide activation and during activity
> >> +
> >> +deactivate_slack	the number of "no contact" frames to ignore before
> >> +			propagating the end of activity events
> >> +
> >> +When the last finger is removed from the device, it sends a number of empty
> >> +frames.  By holding off on deactivation for a few frames we can tolerate false
> >> +erroneous disconnects, where the sensor may mistakenly not detect a finger that
> >> +is still present.  Thus deactivate_slack addresses problems where a users might
> >> +see breaks in lines during drawing, or drop an object during a long drag.
> > 
> > 
> > Without contact tracking, it is hard to imagine activation filtering to work
> > properly. I would advocate to remove this functionality from the driver, and add
> > it in userspace instead.
> > 
> > Henrik
> 
> I don't think its quite time to remove these filters.  There still isn't a
> proper replacement that's readily accessible to most users.  From what I've
> heard many still use the wacom driver to support touch in X.
> 
> Tracking only helps if you increase the activation slack to more than 1 contact
> (the current default), and only if you assume the you will see ghosts span
> multiple frames in two different locations, which may be even less likely than
> seeing a ghost in one spot for two frames.
> 
> Maybe in a few more months or another year, it will make more sense to remove
> the filters from this driver.  In the mean time, is it really preferable to
> leave them undocumented?

Agreed. I have now applied the patch, thanks Rafi.

-- 
Jiri Kosina
SUSE Labs, Novell Inc.
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