Re: vesafb scrolling weirdness

Gerd Knorr (kraxel@goldbach.isdn.cs.tu-berlin.de)
Fri, 10 Jul 1998 23:38:38 +0200


In lists.linux.kernel you write:

>It seems there is definately something weird going on in the screen
>redraw routines when using vesafb. I've looked through the code, but
>not being familiar with it I haven't found any likely cause. The
>problem looks like there is always one line of text _underneath_ the
>one containing the cursor, when the cursor it at the bottom of the
>screen.

>This line of text becomes visible (in the right place) when the screen
>scrolls one line. The line after that one is then hidden, and so
>on. There are also similar weirdnesses in ncurses-based programs.

Have this one here to with the new 108b patches. Older versions work
fine.

vesafb does scrolling by redrawing the the whole screen from the
shadow screen. Becauce most of the time the whole screen is scrolled
and reading from video memory is slow, this works faster than memmove.

It is possible to switch to memmove with "video=vesa:memmove" on the
kernel command line. This fixes the problem, but slows down the console.

The release notes for the patch list some "smart redraw scrolling",
which probably does something like vesafb too. Seems these two
optimations don't like each other...

Maybe the generic fbcon code calles driver's scroll first and updates
the shadow screen later on sometimes? Just a guess, hav'nt checked
the code yet.

Gerd

-- 
Gerd Knorr <kraxel@cs.tu-berlin.de>

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