How to run Weston on specific devices?

[me at beroal.in.ua]

On 07.01.16 10:42, Pekka Paalanen wrote:
>>> Have you tried using the --seat command line argument to make Weston's
>>> DRM-backend pick a seat other than the default "seat0"?
>> Okay, Weston drives "seat1" if given the option "--seat=seat1" and no
>> configuration file. But "seat0" where I start Weston freezes until
>> Weston terminates.
> What do you mean by "freeze"? Black screen? Blank screen? Desktop, but
> no reaction to any input? Does the clock update? Got a log from that,
> does it open any input devices then?
I run "weston-launch" from a virtual terminal/agetty/login/bash. The 
screen does not change, the cursor does not blink. No reaction. I don't 
understand what log should I provide.

>> Why should I run "weston-launch" from a virtual terminal? I would like
>> to run it from "gnome-terminal".
> You cannot run it from X, because the X server is already holding the
> DRM master for the gfx card. The X server must release DRM master
> before Weston can get it, and you do that by switching away from X's VT
> or quitting X. DRM master status is required for controlling KMS
> resources by the Weston DRM-backend.
>
>
But I want to run Weston on a gfx card other than X is running on. I 
have 2 gfx cards.