linux-kernel - [PATCH] mdacon messing up default vc's, set default to vc13-16 again

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Date:	Sat, 03 May 2008 22:09:25 +0200
From:	devzero@....de
To:	Linux-fbdev-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Cc:	adaplas@...il.com, alan@...rguk.ukuu.org.uk, edward@...ian.org,
	jsimmons@...radead.org, Soeren Sonnenburg <kernel@....de>,
	matan@...alib.org
Subject: [PATCH] mdacon messing up default vc's, set default to vc13-16 again

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. 

me 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@....de>

--- drivers/video/console/mdacon.c.orig 2008-05-03 15:47:20.000000000 +0200
+++ drivers/video/console/mdacon.c      2008-05-03 15:55:27.000000000 +0200
@@ -71,13 +71,15 @@

 /* console information */

-static int     mda_first_vc = 1;
+static int     mda_first_vc = 13;
 static int     mda_last_vc  = 16;

 static struct vc_data  *mda_display_fg = NULL;

 module_param(mda_first_vc, int, 0);
+MODULE_PARM_DESC(mda_first_vc, "First virtual console. Default: 13");
 module_param(mda_last_vc, int, 0);
+MODULE_PARM_DESC(mda_last_vc, "Last virtual console. Default: 16");

 /* MDA register values
  */

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