void vga_setdisplaystart(int a);
You should ensure that the memory displayed is actually available on the SVGA card (query memory size with vga_modeinfo(3)) and ensure that it is saved by svgalib during console switches with vga_claimvideomemory(3).
You may only set the bits of the display start address returned by vga_modeinfo(3).
svgalib(7), vgagl(7), libvga.config(5), vga_modeinfo(3), vga_setlogicalwidth(3), vga_claimvideomemory(3)
This manual page was edited by Michael Weller <email@example.com>. The exact source of the referenced function as well as of the original documentation is unknown.
It is very likely that both are at least to some extent are due to Harm Hanemaayer <H.Hanemaayer@inter.nl.net>.
Occasionally this might be wrong. I hereby asked to be excused by the original author and will happily accept any additions or corrections to this first version of the svgalib manual.