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