linux-kernel - Re: Suspend to RAM fault in VT when resuming

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Message-ID: <45F752EF.6030701@canonical.com>
Date:	Tue, 13 Mar 2007 19:42:07 -0600
From:	Tim Gardner <tim.gardner@...onical.com>
To:	Pavel Machek <pavel@....cz>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Suspend to RAM fault in VT when resuming

Pavel Machek wrote:
> Hi1
> 
>> I've chased one of the 'Suspend to RAM' resume problems to a specific
>> line in drivers/char/vt.c, see attached 2.6.21-rc3 diff with
> 
> Has suspend/resume ever worked on that hardware?
> 
>> TRACE_RESUME() instrumentation. The macro scr_writew resolves to '*addr
>> = val', which appears to be causing the problem. I've verified that the
>> pointer is not NULL, but don't know if its really valid. Its pretty
>> tough to tell what is happening, but on a Dell XPS it just hangs. A Dell
>> Precision blinks the keyboard lights.
> 
> It is possible that video is not initialized at that point, and that
> hardware goes seriously unhappy when you access non-existing vga. Does
> it resume ok when you completely disable video support? 
> 
> 
> 								Pavel
> 
> 

Resume works on the Dell XPS with the Ubuntu Edgy release
Ubuntu-2.6.17-10.25 (2.6.17 plus a zillion fixes). Ubuntu's git tree is
rsync://rsync.kernel.org/pub/scm/linux/kernel/git/bcollins/ubuntu-2.6.git.
Ubuntu-2.6.17-8.21 is the first version where resume works, but there
are a boatload of changes in ACPI and SW suspend between that and the
previous tag Ubuntu-2.6.17-7.20. I don't know what made SW suspend work,
but even knowing that won't tell me what broke it again.

I've been avoiding the bisect process because it is quite time consuming
on my slow machine, there is much branch weirdness, and I'm not that
good with git. I thought if I narrowed the failure down to a small chunk
of code in 2.6.21-rc3, then the answer might be obvious. No such luck, huh?

This crash behaves like the video memory space has become unmapped. Is
that possible?

rtg
-- 
Tim Gardner tim.gardner@...ntu.com
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