[LinuxBIOS] RES: RES: RES: VGA Support on AMD DB800

Omar Esteves Duarte Filho duarte at vonbraunlabs.com.br
Wed Jan 2 20:36:08 CET 2008

> First - please - stop using the term 'VGA'.  VGA is a very 
> specific standard for video display 
> (http://en.wikipedia.org/wiki/VGA).  There is no VGA here.  
> By using the term, you muddle the discussion.


> mode_option is only valid when you load the driver as a 
> module.  When running with the driver built in, then you 
> specify the mode on the command line,
> as detailed in Documentation/fb/modedb.txt.   The correct way 
> to specify the
> mode on the command line is as follows:
> video=lxfb:<xres>-<yres>-<bpp>@<refresh>

Yes, my fault! Actually, I did use the correct way of specifying the mode on
the command line. However, when composing the email, i wrongly wrote the
lxfb driver is compiled into the kernel and the current command line is:

kernel          /boot/vmlinuz-
root=UUID=a4e4ac87-c677-45e1-aa21-1e4654feac95 ro console=tty0
console=ttyS0,115200 video=lxfb:640x480 at 60

> I also noted that you were specifying vga=<number> on your 
> command line - if the vesa framebuffer is also installed in 
> your kernel (as it would be with a normal Ubuntu kernel), 
> then that will cause the VESA framebuffer to be loaded first 
> (which would of course, fail).  The lxfb would be loaded as 
> well, but registered as the second framebuffer (if you have 
> your kernel output from dmesg, you should be able to see this happen).
> The fbset you did below would kick the second driver and have 
> it take over the console from the failed primary driver.

VESA VGA Support is -not- enabled. So, lxfb is registered as the first
framebuffer (/dev/fb0):

root at ubuntu-LX800:~# cat /proc/fb
0 Geode LX

> This is the mode that is listed in the file /etc/fb.modes - 
> which is a set of generic timings provided by Ubuntu.  Both 
> timings are actually correct - if you were to run fbset and 
> set the previous timings, they would work.  What you are 
> seeing is a side effect of a poorly configured kernel.
> Jordan

I tried to check both timings sets using "fbset --timings" command. The only
set that works is:

root at ubuntu-LX800:~# fbset -i
mode "640x480-60"
     # D: 25.175 MHz, H: 31.469 kHz, V: 59.940 Hz
     geometry 640 480 640 480 16
     timings 39722 48 16 33 10 96 2
     rgba 5/11,6/5,5/0,0/0

The other set (the "original" one") provides VSYNC=63Hz, instead of 60Hz:

root at ubuntu-LX800:~# fbset -i
mode "640x480-63"
    # D: 25.200 MHz, H: 32.143 kHz, V: 63.150 Hz
    geometry 640 480 640 480 16
    timings 39682 48 8 25 2 88 2
    rgba 5/11,6/5,5/0,0/0


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