Message-ID: <20110705232516.GA4896@core.coreip.homeip.net>
Date:	Tue, 5 Jul 2011 16:25:17 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	Chase Douglas <chase.douglas@...onical.com>, rydberg@...omail.se,
	rubini@...l.unipv.it, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, derek.foreman@...labora.co.uk,
	daniel.stone@...labora.co.uk, olofj@...omium.org
Subject: Re: [PATCH 02/12] Input: synaptics - do not invert y if 0

On Wed, Jul 06, 2011 at 07:15:07AM +0800, Daniel Kurtz wrote:
> On Wed, Jul 6, 2011 at 7:06 AM, Chase Douglas
> <chase.douglas@...onical.com> wrote:
> > On 07/05/2011 03:50 PM, Daniel Kurtz wrote:
> >> On Wed, Jul 6, 2011 at 1:42 AM, Chase Douglas
> >> <chase.douglas@...onical.com> wrote:
> >>>
> >>> On 06/28/2011 10:07 PM, djkurtz@...omium.org wrote:
> >>>> From: Daniel Kurtz <djkurtz@...omium.org>
> >>>>
> >>>> Synaptics touchpads report increasing y from bottom to top.
> >>>> This is inverted from normal userspace "top of screen is 0" coordinates.
> >>>> Thus, the kernel driver reports inverted y coordinates to userspace.
> >>>>
> >>>> In some cases, however, y = 0 is sent by the touchpad.
> >>>> In these cases, the kernel driver should not invert, and just report 0.
> >>>
> >>> Under what cases is y sent as 0, and why do we want to report it as 0 to
> >>> userspace?
> >>
> >> I know of two such cases for the image sensor:
> >>   (1) When all fingers, save the first finger are removed, an AGM
> >> packet with (x=0, y=0, z=0) is sent.
> >>   (2) When all fingers are removed, an SGM packet with (x=0, y=0, z=0) is sent.
> >>
> >> After uploading this patch set, I played with the profile sensor
> >> again, and I also saw it sometimes sends y=1 packets.  I don't know
> >> what those are.
> >>
> >> This is mostly useful for debugging the kernel driver.
> >> When observing the raw position values, the special 0 (and 1?) cases
> >> are more obvious when not inverted.
> >> I think I am misleading in my commit message.  I don't believe these
> >> are actually ever passed through to userspace.
> >
> > If they are set, then they are passed through evdev, unless I'm missing
> > something... Given the cases listed above, it seems like we should be
> > special casing these scenarios. Maybe that means dropping the event or
> > handling finger count transitions or something else.
> >
> > I'm happy with the patch as a cleanup of y inversion, but I don't see
> > the utility of passing y = 0 through. With all the debugging techniques
> > we have (printk, systemtap, perf, ftrace, etc.), I don't think we need
> > this functionality, and it might lead a code reviewer to scratch their
> > head wondering what the point was :).
> 
> I meant if you were to printk y, it is much more obvious to see y=0
> than y=5321 or something like that.
> I don't think this reaches userspace because y=0 packets are usually
> filtered out since z and x are also 0.
> 
> I guess this is the point, actually, that wasn't clear to me in
> Henrik's astute observation:
> We should do the conversion when reporting to userspace.  Thus, only
> do the conversion for packets that aren't already masked!
> 
> I will refactor to an inline function, but put the conversion back in
> the input_report_abs() calls.

Better yet, drop this patch completely. If there is no (or low) pressure
coordinate values are not interesting and shoudl be ignored by both
humans and userspase consumers.

Thanks.

-- 
Dmitry
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