Control fb problem on 8500

[Geert Uytterhoeven]

On Mon, 21 Aug 2000, Michel [iso-8859-1] Dänzer wrote:
> Michael Schmitz wrote:
> > > > That's what I was thinking about. However, I'm not sure that XFree
> > > > supports a display with discontiguous lines in video memory. I think I
> > > > read that somewhere in some mailing list or X doc... Can any of the
> > > > XFree specialists confirm?
> > >
> > > I can speak for XFree86 3.x only, not for 4.x.
> > >
> > > The only way to work with this is to make xres_virtual = xres+0x20. But
> > > then XFree86 will draw into the cursor region, too.
> >
> > I think it used to work without such a hack - some old m68k Macs had the
> > video scan lines start every 1024 bytes but the actual xres was smaller.
> > I'll have to look at the macfb code to see what xres_virtual was set to.
> > I'm sure the X server didn't draw to the offscreen region as that would
> > have caused a bus error (at least the earlier 3.3.x versions didn't.
> > Later X versions drawing beyond xres would in fact explain bus errors
> > some people saw ...).
>
> X 4.0 distincts 3 values:
>
> 'xres'	- physical horizontal resolution of the current mode.
>
> virtualX - horizontal resolution of the virtual screen. Never changes during a
> screen's life.
>
> displayWidth - the length in pixels of each scanline in memory.

I guess this doesn't change during the screen's life neither.

> Unfortunately, the fbdev driver still assumes that displayWidth == virtualX,
> and most other drivers have adapted that assumption (for most of them it's
> right though :) .

Yuk, so we not only have depth/bits_per_pixel mixups but also
virtualX/displayWidth mixups :-(

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/