Re: MTRR vesafb and wrong X performance

[Gerd Knorr]

> size_total is calculated thus:
> 
>     size_total = screen_info.lfb_size * 65536;

That comes almost directly from the BIOS, the screen_info struct is
filled by the real mode boot code (vga.S IIRC).

>     if (vram_total)
>         size_total = vram_total * 1024 * 1024;

The vesafb option to override stuff.

>     if (size_total < size_vmode)
>         size_total = size_vmode;

Thats kida silly, but as I've found some simliar construct in the old
code I left it in to avoid breaking stuff.  Guess there is a reason that
this was there.  I'll take that as proof that broken BIOSes exist which
don't fill screen_info.lfb_size correctly ;)

> or blacklist if there aren't too many perhaps?

Hmm, how identify them?  Map the BIOS and poke around there?
screen_info gives next to no info here.

Maybe it works better to walk the PCI device list, find the correct
gfx card using the framebuffer start address, then double-check the
size by looking at the PCI ressources?

  Gerd

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