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Date:	Mon, 19 Mar 2007 10:15:23 -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:
> On Tue 2007-03-13 19:42:07, Tim Gardner wrote:
>> 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? 
>> 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?
> 
> That seems improbable. It is physical ram, we do not unmap that..
> 

The machine _has_ just come out of BIOS ACPI space. Perhaps PCI
resources for video are hosed. All I can tell for sure is that this one
line appears to cause some kind of crash. I'm working on finding some
1394 resources to see if I can nail this one.

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