libinput pressure detection: clarification for drivers

[Life is hard, and then you die]

On Mon, Mar 06, 2017 at 01:08:48PM +1000, Peter Hutterer wrote:
> On Fri, Mar 03, 2017 at 06:41:31PM -0800, Life is hard, and then you die wrote:
> > 
> > I was testing out the new pressure-based touch detection in libinput
> > (on a new MBP where the sensitivy is such that it's been possible to
> > move the mouse without actually touching the touchpad, so this new
> > feature is very welcome) and realized that it appears the drivers must
> > send actual ABS_MT_PRESSURE or ABS_PRESSURE events. 
> 
> fwiw, "must" is a bit strongly worded here. Yes, libinput currently only
> looks at either of those two but there's no reason we can't look at anything
> else. Main problem is that of time and device availability, almost all
> touchpad devices I see have pressure, few have touch major/minor.
> 
> And the ones that do send relatively random values for those, despite them
> being supposedly well-defined. That's at least true for the touchscreens
> I've seen, not sure on touchpads.

I see. Presumably you need to scale the touch major/minor values to
physical dimensions, but even then they aren't reliable?

> > From reading the
> > kernel documentation at
> > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/plain/Documentation/input/multi-touch-protocol.txt
> > I was under the impression that these events were only needed for
> > devices that didn't provide ABS_MT_TOUCH_MAJOR/ABS_MT_WIDTH_MAJOR .
> > 
> > So my question is basically: am I misreading the above doc, and should
> > drivers then always report pressure events even if they already report
> > touch and width events?
> 
> Do what the kernel doc says and let's add major/minor to libinput, that's
> the long-term plan forward.

Ok. But near term I guess I should go ahead with reporting
ABS_MT_PRESSURE in the driver (Btw., I'm talking about the bcm5974
clone for SPI keyboards+touchpads at
https://github.com/cb22/macbook12-spi-driver).

> > Btw., I noticed that the bcm5974 driver only sends only ABS_PRESSURE
> > (not ABS_MT_PRESSURE) even though it has the ABS_MT_SLOT capability
> > set, so AFAICT the pressure-detection won't work for that device (and
> > the emulation in test/litest-device-bcm5974.c seems misleading since
> > that is sending ABS_MT_PRESSURE events).
> 
> oh, oops. Can you file a bug for that please so I can get that fixed?
> thanks.

Sorry, a bug where? With the bcm5974 driver? It seems to generate
ABS_WIDTH and ABS_PRESSURE for backwards compatibility reasons with
Xorg synaptics drivers, so it's not clear if not generating
ABS_MT_PRESSURE would be considered a bug.


  Cheers,

  Ronald