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

Dmitry Torokhov wrote on 2010-10-22:

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

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>

Greetings,
Michael

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