RE: [PATCH] Input: touchscreen: AD7879: prevent invalid finger data reports

Dmitry Torokhov wrote on 2010-10-22:

On Fri, Oct 22, 2010 at 08:16:48AM +0100, Hennerich, Michael wrote:

quoted

Dmitry Torokhov wrote on 2010-10-22:

quoted

Hi Michael,

On Mon, Oct 18, 2010 at 03:33:24PM +0200,
michael.hennerich@analog.com
wrote:

quoted

From: Michael Hennerich <michael.hennerich@analog.com>

Considering following scenario - the touch is present on the screen
at the beginning of the last conversion sequence, but by the time the
last sequence is finished, the finger is lift off. The AD7879 data
available interrupt signals (DAV) completion, however some X,Y values
are not valid because the screen inputs were floating during the
acquisition.

The AD7877 acts differently here, since it only asserts DAV if
the touch is still present when the conversion sequence finished.

Based on the fact that this can only happen in the last sample of
the repeated conversion sequence. We simply skip the last. (Short
glitches are filtered by the AD7879 internal median and average
filters) This doesn't cause noticeable side effects, since the
minimum conversion interval is 9.44ms. We receive ~100 waypoint
samples per second, so we simply delay the result by 9.44ms.

Actually this patch repeats the first waypoint twice and then

skips

quoted

quoted

the last.

Input core won't actually pass the 2nd instance through. I think the
whole thing should look like the patch below.

I know input core suppresses identical events.
Your patch looks nicer, however it will delay the first response by
one Interrupt. Considering the minimum automatic conversion interval
of 9.44ms
- Not sure how much this really matters.

Acked-by: Michael Hennerich <michael.hennerich@analog.com>

Thanks Michael. I think 10-15ms delay should not be noticeable for
user input, however you have the hardware, any chance you could try and see?

I can confirm that 10ms delay is not noticeable. However this version of the patch
may skip if the touch is very short, so it also implements event filtering of contacts
shorter than 20ms.

Greetings,
Michael

Analog Devices GmbH      Wilhelm-Wagenfeld-Str. 6      80807 Muenchen
Sitz der Gesellschaft Muenchen, Registergericht Muenchen HRB 4036 Geschaeftsfuehrer Thomas Wessel, William A. Martin, Margaret Seif