On 5 Jun 2003, Benjamin Herrenschmidt wrote:

On Thu, 2003-06-05 at 10:19, Sven Luther wrote:

quoted

quoted

quoted

  3) When running X without the UseFBDev option, the colors are good,
  but i get garbage when i return to the console. Not exactly garbage,
  at first it is ok, but when i enter a line or somehow pan the screen,
  the corruption start. Doing a vt switch and back redraws a clean
  screen.

Known problem. This is actually a bit nasty. X doesn't fully restore the
engine state (and it's in fact quite difficult to know in which state
it should restore it) and there's no hook in the fbdev layer for
restoring things like that when switching from KD_GRAPHICS back to
KD_TEXT. I'm thinking about adding such a hook in 2.5. Usually, a VT
switch will trigger a restore of the engine state, at least it will
with my version of the driver.

Mmm, so is this a problem in the X server or in the fbdev driver ? I
understand that you will fix this in the fbdev since you have a more
difficult time doing it in the X driver, but this does mean that the X
driver will do a partial save/restore, and that fbdev will then do a
full save/restore ? Seems overkill to me. We can either fix it in the
fbdev driver (which will know which registers the fbdev needs to backup)
or in the X driver (which will know about which register x needs to
backup).

Not exactly. I'm not sure X can restore the engine state exactly
(maybe it can, but imho, it's a bit overkill). I tend to think that
the fbdev shall do it as it's very much easier. On one side, X would
have to backup & restore an insane amount of registers, on the other
side, fbdev can just re-init the engine to the state it wants in a few
dozen lines of code.

Yes, re-initting the engine is the correct way. IIRC, atyfb does this when text
mode acceleration is re-enabled in fb_var_screeninfo.accel_flags. I.e. when X
leaves graphics mode and switches VT.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@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



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