linux-kernel - Re: [PATCH] fix n900 dts file to work around 4.1 touchscreen regression on n900

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Date:	Fri, 29 May 2015 23:02:59 +0200
From:	Pavel Machek <pavel@....cz>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Felipe Balbi <balbi@...com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Sebastian Reichel <sre@...nel.org>,
	kernel list <linux-kernel@...r.kernel.org>,
	pali.rohar@...il.com, sre@...ian.org, sre@...g0.de,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-omap@...r.kernel.org, tony@...mide.com, khilman@...nel.org,
	aaro.koskinen@....fi, ivo.g.dimitrov.75@...il.com,
	patrikbachan@...il.com
Subject: Re: [PATCH] fix n900 dts file to work around 4.1 touchscreen
 regression on n900

On Fri 2015-05-29 13:48:47, Dmitry Torokhov wrote:
> On Fri, May 29, 2015 at 10:34:56PM +0200, Pavel Machek wrote:
> > Hi!
> > 
> > > > > single DT, you don't even use that property in your driver, and now
> > > > > that you realise you meant something else, you want the code that
> > > > 
> > > > not Pali, Sebastian.
> > > > 
> > > > > actually parse the *right* property and does the right thing, that all
> > > > > other DT agree (and depend on) to be reverted?
> > > > 
> > > > We shouldn't revert, that I agree. But both properties should be parsed.
> > > 
> > > No. If the property is wrong, and nobody parsed it, I do not see any reason to
> > > start now.
> > 
> > Agreed.
> > 
> > But that's not what I'm asking. See a changelog of
> > 3eea8b5d68c801fec788b411582b803463834752 and compare it with what it
> > actually does.
> > 
> > It is buggy. If fuzz is specified but maximum is not, it overwites
> > maximum with zero.
> 
> Yes.
> 
> > 
> > Plus it introduces new failure "if (!test_bit(axis, dev->absbit))".
> 
> That is not a new failure. It actually warns users that they trying to
> specify in DT something that will be ignored by the kernel (because
> without that absbit kernel will ignore all requests to that event code).

What if driver sets the bits after parsing device tree?

> > Plus it fails to distinguish between "value not specified in the dt"
> > and "zero is specified in the dt".
> 
> Yes. I am not sure if we should care and support all permutations (ah, I
> pre-setup fuzz in the driver, but override max on X, and I pre-setup
> max on X, but take fuzz from DT). Maybe we should simply document that
> specifying one parameter for an axis will change the rest of them to be
> 0. Not sure though...

Well, the old code did support all permutations. "cleanups" should not
change such details...
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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