Re: [PATCH 2/2] input: mt: Document the MT event slot protocol (rev4)

Ping Cheng
2010-05-25T16:33:35Z

On Mon, May 24, 2010 at 11:02 AM, Henrik Rydberg <rydberg@euromail.se> wrote:
> Ping Cheng wrote:
>> On Mon, May 24, 2010 at 12:13 AM, Henrik Rydberg <rydberg@euromail.se> wrote:
>>> Ping Cheng wrote:
>>>> What I am thinking is that we only need one SYN_ call for both _MT_
>>>> and regular data combined, which is a call to input_sync() at the end
>>>> of the whole packet. The SYN_MT_ can be replaced by the following
>>>> example, which I think is more "client-friendly". This solution is
>>>> based on the fact that the major difference between type A and type B
>>>> is whether we need to filter the data or not:
>>>>
>>>> ABS_MT_RANDOM 0
>>>> ABS_MT_POSITION_X x[0]
>>>> ABS_MT_POSITION_Y y[0]
>>>> ABS_MT_ RANDOM 1
>>>> ABS_MT_POSITION_X x[1]
>>>> ABS_MT_POSITION_Y y[1]
>>>> SYN_REPORT
>>>>
>>>> input_set_abs_params(input_dev, ABS_MT_RANDOM, 0, 2, 0, 0);
>>>>
>>>> would tell the clients that they can expect two random touches.
>>> And if you do s/RANDOM/SLOT/, you end up with what? ;-)
>>
>> Haha, I know what you are thinking :).
>>
>> Maybe I didn't make my point clear.  I didn't mean to make SLOT
>> backward compatible.  I meant to replace SYN_MT_REPORT event with the
>> ABS_MT_ RANDOM label so we only sync the whole packet once at the end.
>> This way both types of MT_ data follow the same input event reporting
>> flow....
>
> You mean changing the type A protocol, breaking the current code base? That is a
> big no-no.

Hi Henrik,

I saw your new patchset, very much appreciated. There are reasons
that I am not "attacking" your new patches:

1. I don't want to ruin your hard work;
2. It would be easier for others to understand what I am talking
about along this thread.

I came up with another "crazy" idea which doesn't break the existing
type A protocol/code. We leave the existing code as is. However, we
make the new SLOT format support both type A and type B. This unified
approach offers a benefit for future X driver and client developers to
treat both types the same way.

As we've discussed before, the major difference between type A and
type B is the filtering and tracking mechanism. Filtering is tied to
the tracking ID since we do not apply filter to the untracked touch
poinsts. From this point of view, ABS_MT_SLOT doesn't lead to the
filter. The existence of an unique tracking ID triggers the filter.

Pure type A format (no filter applied):

ABS_MT_SLOT 0
ABS_MT_POSITION_X x[0]
ABS_MT_POSITION_Y y[0]
ABS_MT_ SLOT 1
ABS_MT_POSITION_X x[1]
ABS_MT_POSITION_Y y[1]
SYN_REPORT

Pure type B format (filter applied upon the detection of a tracking ID)

ABS_MT_SLOT 0
ABS_MT_TRACKING_ID 45
ABS_MT_POSITION_X x[0]
ABS_MT_POSITION_Y y[0]
ABS_MT_SLOT 1
ABS_MT_TRACKING_ID 46
ABS_MT_POSITION_X x[1]
ABS_MT_POSITION_Y y[1]
SYN_REPORT

Hybrid format (filter applied only when a tracking ID is detected):

ABS_MT_SLOT 0
ABS_MT_POSITION_X x[0]
ABS_MT_POSITION_Y y[0]
ABS_MT_SLOT 1
ABS_MT_TRACKING_ID 46
ABS_MT_POSITION_X x[1]
ABS_MT_POSITION_Y y[1]
ABS_MT_SLOT 2
ABS_MT_TRACKING_ID 20
ABS_MT_POSITION_X x[2]
ABS_MT_POSITION_Y y[2]
SYN_REPORT

So, one protocol covers both cases for the future.

Ping