From: Dmitry Torokhov <dtor_core@ameritech.net>
To: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mousedev: Fix scrollwheel thingy on IBM ScrollPoint mice
Date: Wed, 27 Oct 2004 01:29:49 -0500
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Cc: Vojtech Pavlik <vojtech@suse.cz>, Andrew Morton <akpm@osdl.org>,
       Kim Holviala <kim@holviala.com>
References: <417E0EA8.7000704@holviala.com> <200410261933.50544.dtor_core@ameritech.net> <20041027055059.GB1211@ucw.cz>
In-Reply-To: <20041027055059.GB1211@ucw.cz>
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On Wednesday 27 October 2004 12:51 am, Vojtech Pavlik wrote:
> On Tue, Oct 26, 2004 at 07:33:50PM -0500, Dmitry Torokhov wrote:
> 
> > > > This patch limits the scroll wheel movements to be either +1 or -1 on
> > > > the event -> emulated PS/2 level. I chose to implement it there because
> > > > mousedev emulates Microsoft mice but the real ones almoust never return
> > > > a bigger value than 1 (or -1).
> > > > ...
> > > > +#ifdef CONFIG_INPUT_MOUSEDEV_WHEELFIX
> > > > +				if (value) { value = (value < 0 ? -1 : 1); }
> > > > +#endif /* CONFIG_INPUT_MOUSEDEV_WHEELFIX */
> > > 
> > > This is really not a thing which we can put behind compile-time config.
> > > 
> > > Can we come up with a fix which works correctly on all hardware?  If not,
> > > this workaround will need to be enabled by some sort of runtime detection.
> > > 
> > 
> > Unless someone (Vojtech?) has an objection I think we should always have
> > this workaround activated - after all mousedev provides legacy emulation
> > mostly for XFree/XOrg benefit anyway. Clients accessing data through evdev
> > will see the full picture regardless.
>  
> We can have a workaround for XOrg, but not one like this. This will make
> fast scrolling unreliable. I have standard Microsoft-compatible mice
> which do report more than one scroll tick per report, if you scroll the
> wheel fast enough, and this throws away the extra ticks.
> 
> We would have to split the value into multiple events which would each
> report a 1 or -1.
> 

I have taken a look at XFree/XOrg sources and it seems that they should
not have -1/1 problem but values outside of limits allowed for Intellimouse
or Explorer protocols will cause re-evaluation of protocol mode. We probably
just clamp values to protocol limits (-8/+7 for intellimouse and explorer
modes) and be done with it.

-- 
Dmitry
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