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 21:57:40 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Pavel Machek <pavel@....cz>
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, 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.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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