Re: Bug in vga16fb?

[Petr Vandrovec <vandrove@vc.cvut.cz>]

Ondrej Zajicek wrote:
> Hello
> 
> I tried vga16fb driver in 320x200x4 nonstd mode (on i386 - little endian). In
> this mode framebuffer reports PACKED PIXELS type. Drawing through framebuffer
> is OK, but console is broken - it looks like that even and odd columns are
> exchanged.
> 
> Framebuffer structure of this mode is that even pixel is in high nibble and
> odd pixel is in low nibble.
> 
> It looks like vga16fb use cfbimgblt.c/slow_imageblit in this mode for
> image-blit and this function in CFB4 writes even pixel in low nibble and
> odd pixel in high nibble.
> 
> What is correct framebuffer structure for CFB4 mode?

Unfortunately there is no standard, as CFB4 itself is quite non-standard VGA 
mode.  Some videocards first output low nibble, followed by high, and some do 
otherwise.  I've experimented with this back in 2000, and I've found that Matrox 
Millennium does exactly opposite than some ATI Mach64 card I had in another box 
at that time.

So your only option is providing two CFB4 modes.  Unfortunately I have no idea 
how to autodetect what your hardware actually does without adding camera to the 
system...
							Petr Vandrovec



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