Re: [PATCH] alps: Fix finger jumps on lifting 2 fingers on v7 touchpad

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Wed, May 20, 2015 at 11:16:53AM +0200, Hans de Goede wrote:
> On v7 touchpads sometimes when 2 fingers are moved down on the touchpad
> until they "fall of" the touchpad, the second touch will report 0 for y
> (max y really since the y axis is inverted) and max x as coordinates,
> rather then reporting 0, 0 as is expected for a non touching finger.
> 
> This commit detects this and treats these touches as non touching.
> 
> See the evemu-recording here:
> https://bugzilla.redhat.com/attachment.cgi?id=1025058
> 
> BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1221200
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  drivers/input/mouse/alps.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
> index 745921f..9bc4343 100644
> --- a/drivers/input/mouse/alps.c
> +++ b/drivers/input/mouse/alps.c
> @@ -949,6 +949,11 @@ static void alps_get_finger_coordinate_v7(struct input_mt_pos *mt,
>  	case V7_PACKET_ID_TWO:
>  		mt[1].x &= ~0x000F;
>  		mt[1].y |= 0x000F;
> +		/* Detect false-postive touches where x & y report max value */
> +		if (mt[1].y == 0x7ff && mt[1].x == 0xff0) {
> +			mt[1].x = 0;
> +			/* y gets set to 0 at the end of this function */

I think this is too fragile; I believe we can spare an assignment and
maybe compiler will optimize it out.

I can fix it up locally unless there are objections to having this extra
assignment.

> +		}
>  		break;
>  
>  	case V7_PACKET_ID_MULTI:
> -- 
> 2.4.1
> 

Thanks.

-- 
Dmitry