X11 slowness on vortex86sx

Today I played a bit with Vortex86sx based device again. This time I wanted to get X11 working on it.

In short: it “works”. Default driver should be “sis” but it fails with messages which shows that libpciaccess has a problem on that device:

(EE) SIS(0): Unable to map IO aperture. Invalid argument (22)                                                                
(EE) SIS(0): **************************************************                                                              
(EE) SIS(0):                       ERROR:                                                                                    
(EE) SIS(0): Could not map MMIO area                                                                                         
(EE) SIS(0):                   END OF MESSAGE                                                                                
(EE) SIS(0): **************************************************                                                              
(EE) SIS(0): **************************************************                                                              
(EE) SIS(0):                       ERROR:                                                                                    
(EE) SIS(0): SiSMapMem() failed                                                                                              
(EE) SIS(0):                   END OF MESSAGE                                                                                
(EE) SIS(0): **************************************************                                                              

I switched to “vesa” driver — it works, gives 1280×1024 resolution. But it is so sluggish… Even my few years old Zaurus c760 is faster (I checked how Vortex86sx works with VGA resolution).

Tried also “fbdev” driver — same slowness. All was done with full X.org server not “kdrive” one.