Hi Dmitry,
[ adding more relevant people to the discussion ]
On Apr 23 2015 or thereabouts, Benjamin Tissoires wrote:
> On Apr 23 2015 or thereabouts, Dmitry Torokhov wrote:
> > On Wed, Apr 22, 2015 at 11:45:09AM -0400, Benjamin Tissoires wrote:
> > > Synaptics PS/2 touchpad can send only 2 touches in a report. They can
> > > detect 4 or 5 and this information is valuable.
> > >
> > > In commit 63c4fda3c0bb ("Input: synaptics - allocate 3 slots to keep
> > > stability in image sensors"), we allocate 3 slots, but we still continue
> > > to report the 2 available fingers. That means that the client sees 2 used
> > > slots while there is a total of 3 fingers advertised by BTN_TOOL_TRIPLETAP.
> > >
> > > For old kernels this is not a problem because max_slots was 2 and libinput/
> > > xorg-synaptics knew how to deal with that. Now that max_slot is 3, the
> > > clients ignore BTN_TOOL_TRIPLETAP and count the actual used slots (so 2).
> > > It then gets confused when receiving the BTN_TOOL_TRIPLETAP and DOUBLETAP
> > > information, and goes wild.
> > >
> > > We can pin the 3 slots until we get a total number of fingers below 2.
> > >
> > > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1212230
> >
> > Benjamin, I do not quite like it. It seems that original patch was not
> > quite right and we are adding more workarounds.
>
> Agree. And I am starting to hate more and more the synaptics PS/2 and all
> the PS/2 drivers to be honest :) - trying to fit a heavy load data like
> multitouch in a simple and lightweight protocol like PS/2 is insane...
>
> We are internally trying to figure out if we can finally take advantage
> of the SMBus/RMI4 protocol, but we tried for one year without much
> success.
>
> >
> > Synaptics can only track 2 contacts, correct? Why 2 slots to track them
> > is not enough?
>
> IIRC, the problem was that upon a third finger down, with only 2 slots,
> the fingers were silently inverted in most cases. The thing is that the
> firmware forwards 2 fingers, but not necessarily the two first. So you
> generally get fingers 1+3 so the slot 2 needs to be removed. And that
> means the kernel tracking has to track 3 fingers upon transitions.
>
> This may be completely bullshit and we might not need to use 3 slots at
> all. I'll need to do further experiments to validate which one is best
> then.
>
> I am perfectly fine holding this one up for a little bit more testings
> and then we can decide which one needs to be done (revert or an other
> band-aid).
>
So I carefully recorded each situation (initial with 2 slots, 2 slots
and then with the pinning in this patch*), and I am now convinced that
the pinning is the best sequence that we forward to the user space (best
among the 3).
With 2 slots declared, there are 2 problems:
- the first finger jumps to the position of the 3rd when it lands
- the transition between 2 to 3 fingers goes to a state where the kernel
removes the second finger (while jumping the first to the position of
the 3rd finger), send a sync and then reallocate the first finger
position as the second slot in use
-> that means that user space sees a small transition where the slots
count is 1 while the BTN_TOOL advertise triple tap :/
With 3 slots, we have the problem reported in the rhbz bug #1212230:
- during the transition, the fingers are stable, but we have at most 2
active slots in one frame, which confuses libinput/xorg-synaptics.
With the pinning, the user space is no more confused because BTN_TOOL is
always greater or equal than the active slots.
So I think for now we have 3 possibilities:
1. Just carry this patch, and hope that we will be able to switch the
synaptics device in the non-PS/2 mode
2. Revert to 2 patches and fix the kernel tracking to accept 3 fingers
and return the 2 best matches
3. Revert the use of the kernel tracking at all and re-introduce the
spaghetti code that was here before and hope that all cases where
properly handled.
IMO that the solution 2. is the best, but I can not do it because I
don't understand what the code does. I can guess things but I can not
accurately change it because it is not readable IMO.
(yes, there is also the solution 4: "screw up and let the user space deal
with it", but I'd rather not do that given the history of the multitouch
protocol)
Cheers,
Benjamin
* I tried to put side by side the 3 test cases in the following logs:
(init slots 2, no pinning) | (init slots 3, no pinning) | (init slots 3, pinning)
----------------------------- | ----------------------------- | ---------------------------
------------------------------|----- one finger down -------|----------------------------
| |
ABS_MT_SLOT 0 | ABS_MT_SLOT 0 | ABS_MT_SLOT 0
ABS_MT_TRACKING_ID 53 | ABS_MT_TRACKING_ID 53 | ABS_MT_TRACKING_ID 53
ABS_MT_POSITION_X 2000 | ABS_MT_POSITION_X 2000 | ABS_MT_POSITION_X 2000
ABS_MT_POSITION_Y 2000 | ABS_MT_POSITION_Y 2000 | ABS_MT_POSITION_Y 2000
ABS_MT_PRESSURE 68 | ABS_MT_PRESSURE 68 | ABS_MT_PRESSURE 68
BTN_TOUCH 1 | BTN_TOUCH 1 | BTN_TOUCH 1
ABS_X 2000 | ABS_X 2000 | ABS_X 2000
ABS_Y 2000 | ABS_Y 2000 | ABS_Y 2000
ABS_PRESSURE 68 | ABS_PRESSURE 68 | ABS_PRESSURE 68
BTN_TOOL_FINGER 1 | BTN_TOOL_FINGER 1 | BTN_TOOL_FINGER 1
--- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ----------
| |
... | ... | ...
| |
------------------------------------ second finger down ------------------------------------
| |
--- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ----------
ABS_MT_POSITION_X 2000 | ABS_MT_POSITION_X 2000 | ABS_MT_POSITION_X 2000
ABS_MT_POSITION_Y 2000 | ABS_MT_POSITION_Y 2000 | ABS_MT_POSITION_Y 2000
ABS_MT_PRESSURE 78 | ABS_MT_PRESSURE 78 | ABS_MT_PRESSURE 78
ABS_MT_SLOT 1 | ABS_MT_SLOT 1 | ABS_MT_SLOT 1
ABS_MT_TRACKING_ID 54 | ABS_MT_TRACKING_ID 54 | ABS_MT_TRACKING_ID 54
ABS_MT_POSITION_X 3000 | ABS_MT_POSITION_X 3000 | ABS_MT_POSITION_X 3000
ABS_MT_POSITION_Y 3000 | ABS_MT_POSITION_Y 3000 | ABS_MT_POSITION_Y 3000
ABS_MT_PRESSURE 64 | ABS_MT_PRESSURE 64 | ABS_MT_PRESSURE 64
ABS_X 2000 | ABS_X 2000 | ABS_X 2000
ABS_Y 2000 | ABS_Y 2000 | ABS_Y 2000
ABS_PRESSURE 78 | ABS_PRESSURE 78 | ABS_PRESSURE 78
BTN_TOOL_FINGER 0 | BTN_TOOL_FINGER 0 | BTN_TOOL_FINGER 0
BTN_TOOL_DOUBLETAP 1 | BTN_TOOL_DOUBLETAP 1 | BTN_TOOL_DOUBLETAP 1
--- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ----------
| |
... | ... | ...
| |
------------------------------------ third finger down ------------------------------------
| |
--- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ----------
ABS_MT_SLOT 0 | ABS_MT_SLOT 0 | ABS_MT_SLOT 0
ABS_MT_POSITION_X 4000 | ABS_MT_POSITION_X 2000 | ABS_MT_POSITION_X 2000
ABS_MT_POSITION_Y 4000 | ABS_MT_POSITION_Y 2000 | ABS_MT_POSITION_Y 2000
ABS_MT_PRESSURE 78 | ABS_MT_PRESSURE 78 | ABS_MT_PRESSURE 78
ABS_MT_SLOT 1 | ABS_MT_SLOT 2 | ABS_MT_SLOT 2
ABS_MT_TRACKING_ID -1 | ABS_MT_TRACKING_ID 55 | ABS_MT_TRACKING_ID 55
| ABS_MT_POSITION_X 4000 | ABS_MT_POSITION_X 4000
| ABS_MT_POSITION_Y 4000 | ABS_MT_POSITION_Y 4000
| ABS_MT_PRESSURE 72 | ABS_MT_PRESSURE 72
| ABS_MT_SLOT 1 |
| ABS_MT_TRACKING_ID -1 |
ABS_X 4000 | ABS_X 2000 | ABS_X 2000
ABS_Y 4000 | ABS_Y 2000 | ABS_Y 2000
ABS_PRESSURE 78 | ABS_PRESSURE 78 | ABS_PRESSURE 78
BTN_TOOL_DOUBLETAP 0 | BTN_TOOL_DOUBLETAP 0 | BTN_TOOL_DOUBLETAP 0
BTN_TOOL_TRIPLETAP 1 | BTN_TOOL_TRIPLETAP 1 | BTN_TOOL_TRIPLETAP 1
--- SYN_REPORT (0) ---------- | |
ABS_MT_SLOT 0 | |
ABS_MT_POSITION_X 4000 | |
ABS_MT_POSITION_Y 4000 | |
ABS_MT_PRESSURE 78 | |
ABS_MT_SLOT 1 | |
ABS_MT_TRACKING_ID 55 | |
ABS_MT_POSITION_X 2000 | |
ABS_MT_POSITION_Y 2000 | |
ABS_MT_PRESSURE 72 | |
ABS_X 4000 | |
ABS_Y 4000 | |
ABS_PRESSURE 78 | |
--- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ----------
| |
... | ... | ...
| |
------------------------------------ 3 fingers release ------------------------------------
| |
| |
--- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ----------
| | ABS_MT_SLOT 2
| | ABS_MT_POSITION_X 4000
| | ABS_MT_POSITION_Y 4000
| | ABS_MT_PRESSURE 45
ABS_MT_SLOT 0 | ABS_MT_SLOT 0 | ABS_MT_SLOT 0
ABS_MT_TRACKING_ID -1 | ABS_MT_TRACKING_ID -1 | ABS_MT_TRACKING_ID -1
ABS_MT_SLOT 1 | ABS_MT_SLOT 2 | ABS_MT_SLOT 1
ABS_MT_TRACKING_ID -1 | ABS_MT_TRACKING_ID -1 | ABS_MT_TRACKING_ID -1
| | ABS_X 4000
| | ABS_Y 4000
BTN_TOUCH 0 | BTN_TOUCH 0 | ABS_PRESSURE 45
ABS_PRESSURE 0 | ABS_PRESSURE 0 | BTN_TOOL_FINGER 1
BTN_TOOL_TRIPLETAP 0 | BTN_TOOL_TRIPLETAP 0 | BTN_TOOL_TRIPLETAP 0
--- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ---------- | --- SYN_REPORT (0) ----------
| | ABS_MT_SLOT 2
| | ABS_MT_TRACKING_ID -1
| | BTN_TOUCH 0
| | ABS_PRESSURE 0
| | BTN_TOOL_FINGER 0
| | --- SYN_REPORT (0) ----------
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