linux-kernel - Re: v4.1 to v4.7: regression in tsc2005 driver

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Date:	Tue, 19 Jul 2016 20:34:57 -0500
From:	Michael Welling <mwelling@...e.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Pavel Machek <pavel@....cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	linux-input@...r.kernel.org, pali.rohar@...il.com, sre@...nel.org,
	aaro.koskinen@....fi, ivo.g.dimitrov.75@...il.com,
	patrikbachan@...il.com, serge@...lyn.com
Subject: Re: v4.1 to v4.7: regression in tsc2005 driver

On Tue, Jul 19, 2016 at 05:53:07PM -0700, Dmitry Torokhov wrote:
> On Tue, Jul 19, 2016 at 07:39:08PM -0500, Michael Welling wrote:
> > On Tue, Jul 19, 2016 at 04:51:20PM -0700, Dmitry Torokhov wrote:
> > > On Sun, Jul 17, 2016 at 05:56:36PM -0500, Michael Welling wrote:
> > > > On Sun, Jul 17, 2016 at 10:03:39PM +0200, Pavel Machek wrote:
> > > > > On Sun 2016-07-17 13:51:34, Michael Welling wrote:
> > > > > > On Sun, Jul 17, 2016 at 08:42:09PM +0200, Pavel Machek wrote:
> > > > > > > On Sun 2016-07-17 13:24:45, Michael Welling wrote:
> > > > > > > > On Sun, Jul 17, 2016 at 07:52:57PM +0200, Pavel Machek wrote:
> > > > > > > > > Hi!
> > > > > > > > > 
> > > > > > > > > tsc2005 driver changed input device name, from
> > > > > > > > > 
> > > > > > > > > drivers/input/touchscreen/tsc2005.c:	  input_dev->name = "TSC2005
> > > > > > > > > touchscreen";
> > > > > > > > > 
> > > > > > > > > to "TSC200X touchscreen". Unfortunately, X seems to propagate that
> > > > > > > > > name to userspace, where it is needed to be able to do
> > > 
> > > Technically X _is_ userspace.
> > > 
> > > > > > > > > 
> > > > > > > > > xinput --set-prop --type=int ...
> > > > > > > > > 
> > > > > > > > > with the right arguments to calibrate touchscreen. (Touchscreen is
> > > > > > > > > unusable without calibration).
> > > > > > > > > 
> > > > > > > > > What to do with that?
> > > 
> > > Hmm, I do not think we ever committed for the device names to be stable.
> > > You are supposed to locate touchscreen device based on its properties
> > > and you might need some heuristic if you encounter a system with more
> > > than one such touchscreen.
> > > 
> > > > > > > > 
> > > > > > > > The input_dev name could be passed to the common probe function.
> > > > > > > > 
> > > > > > > > http://lxr.free-electrons.com/source/drivers/input/touchscreen/tsc2005.c#L65
> > > > > > > 
> > > > > > > That would be preffered, I guess.
> > > > > > > 
> > > > > > > How many stable releases are affected?
> > > > > > 
> > > > > > Well this patch is 9 months old now. Lets see.
> > > > > > 
> > > > > > It was introduced in v4.4-rc1. So v4.4, v4.5 and v4.6.
> > > > > 
> > > > > Ok, thanks for the information. I believe changing it back to
> > > > > "TSC2005" version makes sense (and then fixing it in stable).
> > > 
> > > Do we know how many users are affected?
> > 
> > Anyone with an old N900 and the smarts to update the kernel.
> 
> Soo... only Pavel? ;)
> 
> > 
> > > 
> > > > 
> > > > Lets see if the maintainer has any input before I submit a patch.
> > > 
> > > I guess we could also pass the input_id structure to tsc200x_probe, fill
> > > the proper product ID (2004 or 2005) and derive the name form it.
> > >

If we passed the input_dev with the filled product idea it would have to be
allocated in the calling probe functions instead of the common probe.

This will lead to more duplicated code which we jumped through so many hoops
to avoid.

> > 
> > Okay do you really think this should be considered a regression?
> > 
> > Should I go ahead with the patch?
> 
> To "fix" it is a small change so we might as well do that, but I
> probably leave it off stable for now.
> 
> Thanks.
> 
> -- 
> Dmitry