Re: Logitech T650 is unusable since 3.19.0

[Peter Hutterer <peter.hutterer@who-t.net>]

On Mon, Mar 23, 2015 at 10:59:24AM -0400, Benjamin Tissoires wrote:
> Hi,
> 
> On Mon, Mar 23, 2015 at 5:09 AM, Borislav Petkov <bp@alien8.de> wrote:
> > CC people.
> >
> > On Mon, Mar 23, 2015 at 11:21:02AM +0300, Лежанкин Иван wrote:
> >> Hi,
> >>
> >> after update from 3.18.7 to 3.19.x my Logitech touchpad became almost
> >> unusable. I use OpenSUSE Thumbleweed and tried both custom and vanilla
> >> kernels. AFAIK, the problem may come with this changes:
> >> http://lkml.iu.edu/hypermail/linux/kernel/1412.1/03246.html
> 
> Indeed, in 3.19, the touchpad is switched into a "raw" mode where it
> forwards the multitouch points rather than using the mouse emulation
> mode.
> 
> >>
> >> The symptoms are as follows.
> >>
> >> 1. The touch density is twice reduced: I have to make longer finger
> >> motion for a smaller pointer movement. Possibly, it's because the KDE
> >> starts to detect the touchpad as touchpad - and not the mouse as it
> >> was before - and applies some preferences like the pointer
> >> acceleration, etc.
> 
> That's either a xorg-synaptics or a KDE bug. But that's somewhat
> expected. The synaptics driver was written a long time ago, at a time
> where the touchpads were quite small. With a touchpad this big, the
> xorg driver simply reduces the speed thinking that your finger is not
> moving much.

It's probably a synaptics bug, I'll add it to my todo list to test this
locally.

> Fortunately, in libinput (and so xf86-input-libinput too), we take
> into account the resolution and provide a consistent feeling across
> touchpads from different sizes.
> 
> >>
> >> 2. Some gestures stopped to work: 3-finger swipe up, down, left, right
> >> - so, there are no more "history back-forward", "SuperKey", and
> >> "SuperKey + d".
> 
> That's expected too, and I was not expecting people to rely that much
> on these features.
> Again, this should be handled by the upper layer, not by the kernel to
> provide a consistent experience with different touchpads.
> Libinput began to implement a gesture support, and maybe we should
> consider adding the 3 finger swipes to the supported gestures.

fwiw, we have some rough long-term plans to provide touchpad gestures in X,
but nothing implemented yet. libinput already has patches for this on the
list, it's down to getting the API right and then exporting the data through
the X protocol.

Having said that: until this is all in place, touchpad gestures simply won't
work.

> >> 3. Multi-finger tap detection is awful: it doesn't detect 3-finger tap
> >> in 50%, it sometimes detects 2-finger tap instead of click+drag, or
> >> when the second finger is slightly touching the surface.
> 
> That is worrisome. It might be a xorg-synaptics bug or a kernel one.
> We (Peter and I) both have a T650, so I guess we can try to reproduce
> this. We might need you to record some evemu traces of the various
> failures.

indeed, please file a bug on bugs.freedesktop.org and assign it to me (with
evemu recordings please).

Cheers,
   Peter
 
> >> Can anyone make a suggestion what should I do, but to stay on an older
> >> kernel version?
> 
> To sum up, apologies for breaking your current setup. I still believe
> that we should not rely on the firmware to provide gestures because
> this generates kind of random shortcuts that are more or less properly
> handled by the desktop environment.
> That being said, it broke your setup, so I will add a parameter that
> you can pass on boot to disable this mode. It's not ideal though, I
> concede.
> 
> I'll come back to you once I have something you can test.
> 
> Jiri, Peter, Hans, if any of you has a better solution (beside
> reverting the raw mode) or want to add something, please do.
> 
> Cheers,
> Benjamin
>