FB model basic issues (WAS: radeon, apertures & memory mapping)

[Roland Scheidegger]

Ville Syrjälä wrote:
  > I think that making the assumption that all memory is preserved when 
the
> memory layout (virtual resolution and depth) doesn't change is perfectly 
> valid too. That would allow X to do it's Ctrl-Alt-+ and - things without 
> repainting the whole screen.
I'm not sure I agree here, as it's not always true. For instance, the 
radeon has some restrictions whether it can use tiling or not with a 
certain mode (interlace/double scan) thus you need to redraw everything 
anyway (which is exactly why I implemented a driver workaround to 
repaint everything when that happens - in fact the workaround also gets 
rid of the offscreen contents, which is not necessary, but was much 
easier to implement, since I couldn't find an easy way to "invalidate 
the framebuffer"). What's the big deal with repainting everything? It's 
not like you would do 100 mode changes per second so it would be 
performance-critical...

Roland