Control fb problem on 8500

[Michael Schmitz]

> > > 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.
>
>
> 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 :) .

The right assumption would be displayWidth == fix.line_length/bpp (using
xres_virtual would have been some horrible kludge). Now where in the pScrn
struct does the fb.fix struct hide?

	Michael


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