Re: [Linux-fbdev-devel] mode switching on intelfb and non-CRT displays

[Knut P. <Knu...@t-...>]

Hi Tony,

>>What would it take to get intelfb mode switching working with non-CRT
>>displays? 
>>
>Documentation.  Or you can try googling for vesafb-tng.
>  
>
Something like that should be possible even without documentation from 
vendor xyz.

    0: google, read X sources, etc.

    1: Extend a private version of vesafb and xyz-fb with a function 
that dumps all known
    hardware  registers. Call it at the end of the xyz-fb_set_par() 
routine and while loading
    vesafb.

    2. Boot several times (without loading X) and save a vesafb register 
dump for every
    valid vesa mode.

    3. Compare the register dumps and try to be intelligent ;-)  Most 
probably you will
    find that only a few registers differ. Some will change with 
differnt color depths,
    some will change with different vertical and horizontal resolutions. 
Also a clock
    divider needs to be discovered.

    4. Verify your assumptions and release a mode switching xyz-fb driver.

It might also be a good idea to write a little dumpreg program for DOS 
and/or Windows.
If there is e.g. a utility program for DOS that allows you to change the 
refresh rate, it
should be quite easy to identify the clock divider registers.

ypan and ywrap scrolling does help a lot to increase speed. Try to 
identify as many
bits of the crt start address value as possible by instrumenting vesafb. 
Simply call your
register dump function at the end of vesafb_pan_display() for several 
times and have a close
look at the bits changed during scrolling. Don´t start displaying those 
register dumps immediately,
that way you obviously would lock your pc.

cu,
 knut

PS and ONLY for the brave: Write a little DOS program that single steps 
the BIOS, saves all
IO to the vga register range to a buffer and displays it after 
completion of the mode switch.
If the BIOS tries to prevent single stepping in real mode, switch to 
vm86. It´s even possible
(and easier to implement than a vm86 monitor) to use a memory manager 
like qemm386 and
a few lines of assembly code to map a writable copy of the video bios 
image at the place of
the original bios if necessary.