- biosfn_set_video_mode: don't load DAC registers if default palette loading is   disabled. Perform gray scale summing if enabled. - biosfn_perform_gray_scale_summing: switch between DAC read and write mode is   required to make this function work. Maximum DAC value always set to 0x3f.
- biosfn_set_video_mode: don't load DAC registers if default palette loading is
  disabled. Perform gray scale summing if enabled.
- biosfn_perform_gray_scale_summing: switch between DAC read and write mode is
  required to make this function work. Maximum DAC value always set to 0x3f.
qemu/vgabios,qemu/vgabios