EXT: Multiple touchscreen environment with Weston

[Ray, Ian (GE Healthcare)]

> On 17 Jun 2019, at 17.45, Theo BUENO <theo.bueno at actia.fr> wrote:
> 
> Hello everyone,
> 
> I am (relatively) new Weston user working with industrial embedded Linux systems. I am seeking for advice regarding a Weston use case.
> 
> I have been trying to understand how would one map touchscreens to unique displays on a system which has several touchscreen displays.
> It is my understanding that prior to Weston 1.7, it could be done via the WL_OUTPUT udev variable for each touchscreen.
> 

We are using Weston 6 with libinput 1-13.0 and we use WL_OUTPUT for this purpose.

Sample log output:

Jun 19 14:17:48 GE0040973102BC weston[305]: [14:17:48.764] event1  - DIALOGUE INC PenMount USB: is tagged by udev as: Touchscreen                            
Jun 19 14:17:48 GE0040973102BC weston[305]: [14:17:48.765] event1  - DIALOGUE INC PenMount USB: device is a touch device                                     
:
Jun 19 14:17:48 GE0040973102BC weston[305]: [14:17:48.913] associating input device event1 with output LVDS-1 (LVDS-1 by udev)                               

And UDEV rule:

SUBSYSTEM=="input", KERNEL=="event[0-9]*", ATTRS{modalias}=="usb:v14E1p6000*", … , ENV{WL_OUTPUT}="LVDS-1"


> Now with more recent versions of Weston, by reading through documentation and code, it is also my understanding that such a use case is addressed via logical seats (WL_SEAT) or through physical seats (ID_SEATS) on a multi-compositor/GPU design.
> 
> Problem is, on the embedded platform I am working on (NXP i.MX6), there can only be one compositor instance bound to the GPU driving multiple displays. With DRM support, I believe assigning a "seat" option to each "output" entry in weston configuration is enough to constrain each touchscreen to their respective displays. Unfortunately, on i.MX6 there is no DRM support with proprietary drivers. The only available backend is fbdev, which after code review does not seem to allow for multiple seat configuration on the same weston instance.
> 
> Am I correct to assume that my only option from here is either to:
> 1) Bring multi-seat support to fbdev backend
> 2) Move to free drivers with DRM support
> 
> Have I missed something / Are my assumptions correct ?
> 
> Many thanks and best regards,
> Théo Bueno.
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