Re: Touchpad problems with 2.6.11-rc2

[Peter Osterlund <petero2@telia.com>]

On Wed, 2 Feb 2005, Dmitry Torokhov wrote:

> On Wed, 02 Feb 2005 13:52:03 -0800 (PST), Peter Osterlund
> <petero2@telia.com> wrote:
> >
> >        if (mousedev->touch) {
> > +               size = dev->absmax[ABS_X] - dev->absmin[ABS_X];
> > +               if (size == 0) size = xres;
>
> Sorry, missed this piece first time around. Since we don't want to
> rely on screen size anymore I think we should set size = 256 *
> FRACTION_DENOM / 2 if device limits are not set up to just report raw
> coords. What do you think?

I think that this case can't happen until we add support for some other
touchpad that doesn't set the absmin/absmax variables. Both alps and
synaptics currently set them.

However, the fallback value should definitely not depend on
FRACTION_DENOM, since this constant doesn't affect the mouse speed at all.
It only affects how accurately we store the fractional part of dx and dy.
Ideally FRACTION_DENOM should be as large as possible without causing
arithmetic overflow. In practice, 128 seemed to be plenty enough.

So, the fallback value should be set to the estimated absmax-absmin value
for the hypothetical future touchpad driver that also hypothetically
doesn't set this value itself. I have no idea how to estimate this value
though, which is why I just used xres. ;)

-- 
Peter Osterlund - petero2@telia.com
http://web.telia.com/~u89404340