linux-kernel - Re: X display shift with disabled console blanking

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Message-Id: <1178032840.5331.2.camel@daplas>
Date:	Tue, 01 May 2007 23:20:40 +0800
From:	"Antonino A. Daplas" <adaplas@...il.com>
To:	James Pearson <james-p@...ing-picture.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: X display shift with disabled console blanking

On Tue, 2007-05-01 at 13:17 +0100, James Pearson wrote:
> Antonino A. Daplas wrote:
> > On Mon, 2007-04-30 at 13:58 +0100, James Pearson wrote:
> > 
> >>Antonino A. Daplas wrote:
> >>
> >>>On Fri, 2007-04-27 at 18:08 +0100, James Pearson wrote:

> It does indeed seem that the switching back and forth between text and 
> graphics does appear to be part of the issue - in my previous testing I 
> probably did do this (but didn't include this in my recipe above) - so 
> here is a new 'recipe' that shows the problem (for me)
> 
> boot to run level 3
> 
> if not root, then make sure /dev/console is writeable
> 
> login and type:
> 
> setterm -blank 0
> 
> start X
> 
> type into an xterm:
> 
> while true; do echo "" > /dev/console; usleep 100000; done
> 
> while the above loop is running switch to the text console and back 
> again (Ctrl-Alt-F1 then Ctrl-Alt-F7)
> 
> ... and the screen will be shifting (and wrapping) to the left.
> 

Okay, this makes me see the problem more clearly.  It looks like that
vt/console layer is unreliable in terms of checking for the
text/graphics mode of the current console.  Instead of auditing the
console code, I'll just have vgacon check for the mode.  Try the
attached patch and let me know if it helps. 

Tony

View attachment "vgacon.diff" of type "text/x-patch" (651 bytes)