FBIOPUT_VSCREENINFO and modelines

问题

I am trying to change the screen configuration with FBIOPUT_VSCREENINFO, but I do not have a clue how to compute:

__u32 pixclock;                 /* pixel clock in ps (pico seconds) */
__u32 left_margin;              /* time from sync to picture    */
__u32 right_margin;             /* time from picture to sync    */
__u32 upper_margin;             /* time from sync to picture    */
__u32 lower_margin;
__u32 hsync_len;                /* length of horizontal sync    */
__u32 vsync_len;

(see: http://lxr.free-electrons.com/source/include/linux/fb.h#L245 ) for the fb_var_screeninfo struct from a given modeline. I tried various alternatives following:

http://www.arachnoid.com/modelines/index.html

but I never get the values of

http://lkml.indiana.edu/hypermail/linux/kernel/9902.0/1388.html

I guess pixclock can be computed with KHZ2PICOS, the remaining I don't seem to get right. Trying the ioctl with my guesswork fails.

Thanks ahead.