mdacon incorrectly detects MDA hardware on systems without such graphics card.
One may load this module by chance, for example when doing some systematical
module-testing, and if there is no Monochrome Display Adapter attached ,
module init renders vc1-16 completely unusable.
I and others have run into this more than once. see [Bug 224522 - modprobe
mdacon freezes machine -> https://bugzilla.novell.com/show_bug.cgi?id=224522 ]
for example
Apparently proper MDA detection seems to be broken for a long time - seems to
be related to those #ifdef TEST_MDA_B statements added by Edward Betts.
this commit back in 2002 made things even worse :
http://git.kernel.org/?p=linux/kernel/git/tglx/history.git;a=commit;h=c72757b49c88914433244757fb4967fc63546685
It changed default vc allocation from 13-16 to 1-16 for no apparent reason
(!?) , and with that (and without X), mdacon grabs the vc you`re currently
sitting on and locks you out.
this is from Kconfig :
>config MDA_CONSOLE
> depends on !M68K && !PARISC && ISA
> tristate "MDA text console (dual-headed) (EXPERIMENTAL)"
> ---help---
> Say Y here if you have an old MDA or monochrome Hercules graphics
> adapter in your system acting as a second head ( = video card). You
> will then be able to use two monitors with your Linux system. Do not
> say Y here if your MDA card is the primary card in your system; the
> normal VGA driver will handle it.
As we can see mdacon is just meant as an additional driver for dual-head
setup, and since kernel 2.4.36 still defaults to vc13-16 , setting the default
back to that value again shouldn`t do any harm.
Hereby i'm reverting that change, setting default back to to vc13-16 again.
Besides the fact that mdacon may be rarely or never be used these days and
could perhaps put to trash anyway (pre-dinosaur hardware!), indeed this is not
a real solution, but at least it removes the unfortunate side-effect of
messing up the vc you`re working on.
Signed-off-by: Roland Kletzing <devzero@web.de>
Cc: James Simmons <jsimmons@infradead.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: Tim Schmielau <tim@physik3.uni-rostock.de>
Cc: Jan Engelhardt <jengelh@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
0b9cf3aa6b