OSELAS BSP, lcd parameters

i'm using the OSELAS BSP on a mini6410.   i have an 800 x 480 LCD attached,
but i can't get anything to appear on the screen.   i found the code in 
mach-mini6410.c that sets up the LCD parameters. i selected the set for the
800x480 screen.  when the kernel boots, i run fbset and the parameters
match what i have them set to in code.   they seem to make sense, and i
checked the timings with an oscilloscope.   i tried two different LCDs. 
nothing at all on the screen, even the backlight doesn't seem to work.    

before trying the larger screen, i used a QVGA screen with the 480x272
parameter set in the code.   when i would run fbtest, i could see patterns
displayed on the screen.   they were however mismatched to the screen, as
if the vsync and/or hsync parameters were incorrect.  

so, question-   how to determine what parameters to give to fbset and/or
code to set up a particular LCD?   and might i be correct in assuming the
problem with my 800x480 lcd does not have it's backlight turned on?

The timing parameter for the 7" 800x480 display coming from the vanilla
kernel. I only have a 480x272 display to test. From my notes your display
should be an AT070TN83. Can you check if the timing matches the datasheet?
http://www.friendlyarm.net/dl.php?file=AT070TN83.pdf

the problem is definitely the backlight.   running with uboot, the  display
we are using works fine, and the backlight is on.   with the OSELAS BSP the
backlight is turned off for some reason.   the parameters we're using are:

.win_mode  = {  /* 7.0" 800x480 */
      .left_margin  = 48,
      .right_margin  = 40,
      .upper_margin  = 7,
      .lower_margin  = 5,
      .hsync_len  = 40,
      .vsync_len  = 40,
      .xres    = 800,
      .yres    = 480,
    },

it looks as if the timing parameters for the backlight are derived somehow,
and if they don't match what the system is capable of, it simply turns the
backlight off.

the LCD is an s70-1125

The backlight of the 480x272 display unit is controlled via a simple GPIO.
Don't know how to control the backlight at the 800x480 display unit.