Problems with the atyfb driver on Power Mac G3

Geert Uytterhoeven Geert.Uytterhoeven at
Mon Aug 16 17:12:54 EST 1999

On Sun, 15 Aug 1999, Eric Dorland wrote:
> >At 4:28 PM -0400 8/15/99, Eric Dorland wrote:
> >>So now atyclk works, and through some experimenting, I've found that
> >>changing the dsp_on value from 24 to 29 removes all the snow I have been
> >>experiencing, without any noticeable slow down. Hooray! Now, the problem is
> >>that this value does not get retained when switching virtual consoles, ie
> >>whenever I switch virtual consoles or start X the dsp_on value gets reset
> >>back to 24. How can I get this value to stay fixed? Should I just hardcode
> >>it into my own kernel compile?
> >
> >Probably not.  Whenever you change video modes, dsp_on and dsp_off are
> >recalculated from the new parameters; a fixed value will not be right for
> >all situations.
> You're right of course. I would have to modify the calculation in some way.
> Any ideas how?

The first thing is to repeat the experiment with a few samples of the set of
zillions of video modes. Then you have to try to find a relation between all
parameters. aty_dsp_gt() in drivers/video/atyfb.c may be good start, just
assume some of the hardcoded values there are wrong.

If you find the Magic Formula, just let us know :-)

> >If you use the exact same mode (and I mean exact) on all VCs (including the
> >one X is running on), no mode switch will be performed when you change VCs,
> >which should preserve your custom dsp_on setting.
> This, unfortunately, does not seem to be the case. I am using the smae mode
> in all my VCs and X and the dsp_on setting is not preserved. I think that
> the atyfb driver gets re-intialized each time I change VCs.

Atyfb always reprograms the video mode. The optimization of not doing that
wasn't implemented yet.



Geert Uytterhoeven                     Geert.Uytterhoeven at
Wavelets, Linux/{m68k~Amiga,PPC~CHRP}
Department of Computer Science -- Katholieke Universiteit Leuven -- Belgium

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