linux-kernel - Re: 4.1 touchscreen regression on n900 -- pinpointed [was Re: linux-n900 v4.1-rc4]

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Date:	Fri, 29 May 2015 22:29:39 +0200
From:	Pavel Machek <pavel@....cz>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Sebastian Reichel <sre@...nel.org>,
	kernel list <linux-kernel@...r.kernel.org>,
	dmitry.torokhov@...il.com,
	Pali Rohár <pali.rohar@...il.com>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
Subject: Re: 4.1 touchscreen regression on n900 -- pinpointed [was Re:
 linux-n900 v4.1-rc4]

On Fri 2015-05-29 21:57:40, Maxime Ripard wrote:
> On Fri, May 29, 2015 at 09:25:05PM +0200, Pavel Machek wrote:
> > On Fri 2015-05-29 21:08:16, Pavel Machek wrote:
> > > Hi!
> > > 
> > > > mh I remember having problems with tsc2005 before. It helped to
> > > > reset the controller (should actually happen automatically when it
> > > > hangs, but I'm not sure, that it actually works).
> > > 
> > > Ok, I did some more testing, and found out rather bogus values in
> > > evtest:
> > > 
> > > Input device name: "TSC2005 touchscreen"
> > > Supported events:
> > >   Event type 0 (EV_SYN)
> > >   Event type 1 (EV_KEY)
> > >   Event code 330 (BTN_TOUCH)
> > >   Event type 3 (EV_ABS)
> > >   Event code 0 (ABS_X)
> > >   Value   2514
> > >  Min        0
> > >  Max        0
> > >  Fuzz       4
> > > 
> > > Which made me go through the git logs, and these patches looked
> > > suspicious. After a revert... yes, touchscreen works as well as it
> > > worked before.
> > > 
> > > 0a363a380954e10fece7cd9931b66056eeb07d56
> > > 3eea8b5d68c801fec788b411582b803463834752
> > > 
> > > (It is impossible to revert just 3eea..)
> > 
> > Hmm, I see:
> > 
> >                 touchscreen-max-x = <4096>;
> >                 touchscreen-max-y = <4096>;
> > ...that's n900 dts.. this should be size-x/size-y... so we have a bug
> > in dts.
> > 
> > But the 3eea8b5d68c801fec788b411582b803463834752 is buggy, it should
> > not overwrite ->maximum for axis it has no devicetree data for.
> 
> What do you mean? touchscreen-max-* _is_ device tree data for an axis.
> 
> > Maybe replacing
> > 
> > +       if (maximum || fuzz)
> > 
> > in 3eea to (maximum && fuzz)... would help, but it is late in the
> > cycle now, so I'd suggest just reverting 3eea8b.
> 
> No, both maximum and fuzz are optional. You can perfectly have one
> without another.

Yes, and after your "cleanup", you overwrite maximum with zero with
fuzz is specified.

->maximum contained 4096 before, your code sees that it is not
specified in the device tree, and you go ahead and replace ->maximum
with 0, anyway.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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