[Libdlo] Linux DispayLink issues

Martin Decky martin at decky.cz
Tue Mar 15 07:34:57 PDT 2011

> In case of wireless USB, device connection is more complicated task then
> in usual USB. So we want be able to connect wireless USB video card to
> host while X server is running.

Yes, sure. And this is exactly the use case which is not supported by 
the current X server. Linux kernel will recognize the new USB video card 
on connection, you can even start a new instance of the X server on it, 
but there is no way how to "plug" it into the running instance of the X 

> Is it possible to implement special x-driver which will care about plug
> and play issue of USB/wireless USB connected video cards?

Technically, yes. Such "wrapper" driver might be a slightly better 
solution than all the current approaches, it might even allow to do such 
"tricks" with the DisplayLink devices which are currently only possible 
in Windows (like using the power of the primary GPU(s) for 3D 
acceleration of the DisplayLink output).

But it will also introduce some overhead even in the case there is no DL 
device connected.

I think, for the long run, it is simply needed to improve the core X 
server to allow much higher degree of run-time (re)configuration. I 
don't want to be a fault-finder, but it's really a shame that the X 
server cannot change the BPP while running. 15 years since Windows can 
do it quite reliably ..

BTW: Some two three years ago people were talking about a future version 
of XRandR (1.4 or something) which should bring multi-GPU support and 
such stuff. Does anybody know what is the current status of these great 

Best regards

Martin Decky

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