Re: PROBLEM: Apple external Trackpad event timestamps are jittery (regression)

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Thanks for following up!

I took Peter's advice and used 'libinput recrod' to get some logs.

I tested both a 1st gen as well as a 2nd gen Apple external trackpads.
While the 1st gen is Bluetooth-only, the 2nd gen can be connected over
both Bluetooth and USB.

The 2nd gen external trackpad had no jitter, regardless if used over
Bluetooth or USB.

Following is a snippet of a 1st gen touchpad, showing only SYN_REPORT
lines for brevity.
This was taken on a kernel with the regression:

    - [  7, 526745,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  7, 537376,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  7, 540141,   0,   0,       1] # ------------ SYN_REPORT (1)
---------- +3ms
    - [  7, 540141,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +0ms
    - [  7, 560065,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +20ms
    - [  7, 571556,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  7, 580125,   0,   0,       1] # ------------ SYN_REPORT (1)
---------- +9ms
    - [  7, 580125,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +0ms
    - [  7, 594466,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +14ms
    - [  7, 604987,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +10ms
    - [  7, 616458,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +12ms
    - [  7, 624124,   0,   0,       1] # ------------ SYN_REPORT (1)
---------- +8ms
    - [  7, 624124,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +0ms
    - [  7, 639259,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +15ms
    - [  7, 650772,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  7, 660130,   0,   0,       1] # ------------ SYN_REPORT (1)
---------- +10ms
    - [  7, 660130,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +0ms

Now a snippet of the 2nd gen trackpad, over Bluetooth, same kernel:

    - [  9, 584965,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  9, 595860,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  9, 607147,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +12ms
    - [  9, 618610,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  9, 630279,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +12ms
    - [  9, 641047,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  9, 652429,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  9, 664148,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +12ms
    - [  9, 674600,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +10ms
    - [  9, 686040,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +12ms
    - [  9, 697808,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  9, 709277,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +12ms
    - [  9, 719649,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +10ms

I'm entirely clueless with regard to the input device protocols,
however it is apparent that the 2nd gen trackpad has only SYN_REPORT
(0) in its log, while the 1st gen has both SYN_REPORT (0) and
SYN_REPORT (1).

Last is a snippet of the 1st gen, this time on a kernel with my hack -
so should behave as before the regression:

    - [  6, 243965,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  6, 254576,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  6, 257637,   0,   0,       1] # ------------ SYN_REPORT (1)
---------- +3ms
    - [  6, 265675,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +8ms
    - [  6, 277512,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +12ms
    - [  6, 288059,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  6, 297642,   0,   0,       1] # ------------ SYN_REPORT (1)
---------- +9ms
    - [  6, 299646,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +2ms
    - [  6, 310849,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  6, 322000,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +12ms
    - [  6, 333265,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +11ms
    - [  6, 337681,   0,   0,       1] # ------------ SYN_REPORT (1)
---------- +4ms
    - [  6, 344588,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +7ms
    - [  6, 356921,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +12ms
    - [  6, 366979,   0,   0,       0] # ------------ SYN_REPORT (0)
---------- +10ms

Here it seems that if we add the delta from each SYN_REPORT (1) to the
delta of the following SYN_REPORT (0) we get sane timestamps.

I also tested a USB mouse, and the timestamps were Ok.
So to summarize my limited finding, only the 1st gen Apple external
touchpad seems to be affected.

Entire logs:

https://drive.google.com/open?id=1nUNf2uOQPvFw_kE8h4mZB0c80kj3hu4F
Gen1, after regression
https://drive.google.com/open?id=1pr508bqeax1Csle2HQuLcuXwinWksdjo
Gen2, after regression
https://drive.google.com/open?id=1W0XekSNyf1i-Um-VqxDJuMmJoWAGXIG5
Gen1, before regression

Please let me know if I there is anything else I can do to help.

Best regards,
Yariv

On Tue, May 12, 2020 at 8:19 AM Peter Hutterer <peter.hutterer@xxxxxxxxx> wrote:
>
> On Mon, May 11, 2020 at 01:11:18PM -0700, Dmitry Torokhov wrote:
> > Hi,
> >
> > On Mon, May 11, 2020 at 09:18:15AM +0300, Yariv wrote:
> > > Using a vanilla installation of Ubuntu 20.04 (kernel v5.4), the
> > > timestamps of input events from my Apple "Magic Trackpad" - 1st
> > > generation, connected over Bluetooth - are jittery.
> > > This is a kernel regression. I bisected the bug.
> >
> > Do you see the same jitter when connected over USB? Can you also see if
> > there is similar jitter when you parse timestamps of SYN_RPEORT events
> > from "evtest"?
> >
> > Could you post a sample of events generated by device (via evtest)?
>
> unrelated, but I really recommend using 'libinput record' these days since
> it can be replayed (libinput replay) or analysed easier (it's YAML).
> Also, it prints delta times into the recording so you can immediately check
> those without having to parse them, e.g.:
>
>   - evdev:
>     - [  0, 375974,   2,   0,       5] # EV_REL / REL_X                     5
>     - [  0, 375974,   2,   1,      -2] # EV_REL / REL_Y                    -2
>     - [  0, 375974,   0,   0,       0] # ------------ SYN_REPORT (0) ---------- +8ms
>
> Cheers,
>    Peter
>



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