linux-kernel - RE: [PATCH] Software Suspend: Fix suspend when console is in VT_AUTO/KD

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Message-ID: <DBC923D919FAB345973A94E6E194E849043808E0@yvrmail01.itc.intrinsyc.com>
Date:	Fri, 9 Mar 2007 08:10:56 -0800
From:	"Andrew Johnson" <ajohnson@...rinsyc.com>
To:	"Matthew Garrett" <mjg59@...f.ucam.org>,
	"Pavel Machek" <pavel@....cz>
Cc:	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] Software Suspend: Fix suspend when console is in VT_AUTO/KD_GRAPHICS mode

Matthew Garrett wrote: 
> On Fri, Mar 09, 2007 at 10:08:05AM +0100, Pavel Machek wrote:
> 
> > So... if current console is graphical, we leave X accessing the
> > console... That's bad, because video state is not going to be
> > restored...?
> 
> A graphical console is not necessarily X. Is there any requirement for
> there to be a single VT that isn't in text mode? The vt switching is
> a hack, we shouldn't make life difficult for people who have their own
> userspace code that's entirely capable of restoring video state on its
> own.

The problem actually comes about when using Qtopia Phone Edition (QPE)
on a PXA270. QPE puts the console into VT_AUTO+KD_GRAPHICS mode and
writes directly to the framebuffer from then on.  In this mode the
kernel correctly disallows a console change, as QPE is not getting
notification of a console change and thus does not know when to repaint
the screen. 

AFAIK, X uses VT_PROCESS+KD_GRAPHICS mode, so it gets notification of a
change to and from the X console, thus it knows when to repaint the
screen.

I think you can test this by changing the mode of a text console to
KD_GRAPHICS using the KDSETMODE ioctl, then attempting to change to
another text console using chvt.

-- Andrew
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