linux-kernel - Re: Fix sudden warps in mousedev

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Date:	Sun, 25 Mar 2007 23:19:38 -0400
From:	Dmitry Torokhov <dtor@...ightbb.com>
To:	Pete Zaitcev <zaitcev@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-input@...ey.karlin.mff.cuni.cz
Subject: Re: Fix sudden warps in mousedev

On Sunday 25 March 2007 14:19, Pete Zaitcev wrote:
> On Sun, 25 Mar 2007 01:34:02 -0400, Dmitry Torokhov <dtor@...ightbb.com> wrote:
> 
> > > +                * Without this, a touchpad may report an unchanged position,
> > > +                * then a sync. The input_event() eats the position report, but
> > > +                * lets the sync through. We increment pkt_count and leave 
> > > +                * a stale position in the ring. If a future reference to fx(2)
> > > +                * hits the stale position, a large dx is reported, and the
> > > +                * pointer warps across the screen.
> > > +                */
> > > +               dev = mousedev->handle.dev;
> > > +               fx(0) = dev->abs[ABS_X];
> > > +               fy(0) = dev->abs[ABS_Y];
> > 
> > I do not like input hanlders poking into input devices... Can't we just
> > reset pkt_count at the beginning of the touch to get rid of stale data?
> 
> The pkt_count is zero at the moment of assignment above.

Riiight... Of course you are right...

I tried to reproduce warping on console but could not for some reason. Could you
please try the patch below and tell me if it fixes the problem for you?

-- 
Dmitry

Signed-off-by: Dmitry Torokhov <dtor@...l.ru>
---

 drivers/input/mousedev.c |   51 +++++++++++++++++++++++------------------------
 1 files changed, 26 insertions(+), 25 deletions(-)

Index: work/drivers/input/mousedev.c
===================================================================
--- work.orig/drivers/input/mousedev.c
+++ work/drivers/input/mousedev.c
@@ -124,32 +124,33 @@ static void mousedev_touchpad_event(stru
 	int size, tmp;
 	enum { FRACTION_DENOM = 128 };
 
-	if (mousedev->touch) {
-		size = dev->absmax[ABS_X] - dev->absmin[ABS_X];
-		if (size == 0)
-			size = 256 * 2;
-
-		switch (code) {
-			case ABS_X:
-				fx(0) = value;
-				if (mousedev->pkt_count >= 2) {
-					tmp = ((value - fx(2)) * (256 * FRACTION_DENOM)) / size;
-					tmp += mousedev->frac_dx;
-					mousedev->packet.dx = tmp / FRACTION_DENOM;
-					mousedev->frac_dx = tmp - mousedev->packet.dx * FRACTION_DENOM;
-				}
-				break;
+	switch (code) {
+		case ABS_X:
+			fx(0) = value;
+			if (mousedev->touch && mousedev->pkt_count >= 2) {
+				size = dev->absmax[ABS_X] - dev->absmin[ABS_X];
+				if (size == 0)
+					size = 256 * 2;
+				tmp = ((value - fx(2)) * (256 * FRACTION_DENOM)) / size;
+				tmp += mousedev->frac_dx;
+				mousedev->packet.dx = tmp / FRACTION_DENOM;
+				mousedev->frac_dx = tmp - mousedev->packet.dx * FRACTION_DENOM;
+			}
+			break;
 
-			case ABS_Y:
-				fy(0) = value;
-				if (mousedev->pkt_count >= 2) {
-					tmp = -((value - fy(2)) * (256 * FRACTION_DENOM)) / size;
-					tmp += mousedev->frac_dy;
-					mousedev->packet.dy = tmp / FRACTION_DENOM;
-					mousedev->frac_dy = tmp - mousedev->packet.dy * FRACTION_DENOM;
-				}
-				break;
-		}
+		case ABS_Y:
+			fy(0) = value;
+			if (mousedev->touch && mousedev->pkt_count >= 2) {
+				/* use X size to keep the same scale */
+				size = dev->absmax[ABS_X] - dev->absmin[ABS_X];
+				if (size == 0)
+					size = 256 * 2;
+				tmp = -((value - fy(2)) * (256 * FRACTION_DENOM)) / size;
+				tmp += mousedev->frac_dy;
+				mousedev->packet.dy = tmp / FRACTION_DENOM;
+				mousedev->frac_dy = tmp - mousedev->packet.dy * FRACTION_DENOM;
+			}
+			break;
 	}
 }
 
-
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