[linux-fbdev] some modes "default" solutions

Geert Uytterhoeven geert at geert.cs.kuleuven.ac.be
Sun Feb 14 01:10:09 EST 1999

On Fri, 12 Feb 1999, Brad Midgley wrote:
> I have been experimenting to try to find out when and why modes "default"
> doesn't work with Xfb.
> 1. modes default is incompatible with acceleration provided by Xfb.
> problems range from messed up colormaps to a white screen pocked with
> artifacts. if you need modes default, turn off acceleration:
> Section "Device"
>     Identifier "Linux Frame Buffer Device"
>     Option "noaccel"
> EndSection

That's strange. I have no explanation for that.

> 2. if you run vmode and it reports something like "0 32" for the current
> mode, Xfb will come up with an oversize virtual screen if it's run with
> modes default. however, if vmode comes up with something like "15 32" then
> the virtual screen size will match the real screen size. 

By default atyfb enables a virtual screen to speed up text scrolling.
With `mode default' XF68_FBDev will use this virtual screen, unless you
override the virtual screen size with `Virtual x y' in your XF86Config.

> unfortunately, the os is not setting the first parameter correctly at
> startup, so the only way to have vmode return something sensible is to use
> it to set the value, eg by running vmode 15 32 at startup.
> i am going to look into why the os isn't setting the first value properly.

Vmode returns `0' for the video mode if you're using a mode that's not one of
the 20 MacOS modes.

But you're right: the vertical virtual screen size must not be considered to
find out the MacOS vmode number. What about

--- drivers/video/macmodes.c.orig	Sun Jan 24 15:04:06 1999
+++ drivers/video/macmodes.c	Sat Feb 13 15:09:19 1999
@@ -363,7 +363,7 @@
 	const struct mac_mode *mode = mac_modes_inv[i];
 	if (var->xres > mode->xres || var->yres > mode->yres)
-	if (var->xres_virtual > mode->xres || var->yres_virtual > mode->yres)
+	if (var->xres_virtual > mode->xres)
 	if (var->pixclock > mode->pixclock)

> i'm observing both these behaviors on an imac and on a powermac 7500 with
> an ati xclaim vr board. 

Both use atyfb.



Geert Uytterhoeven                     Geert.Uytterhoeven at cs.kuleuven.ac.be
Wavelets, Linux/{m68k~Amiga,PPC~CHRP}  http://www.cs.kuleuven.ac.be/~geert/
Department of Computer Science -- Katholieke Universiteit Leuven -- Belgium

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