linux-kernel - Re: I need some serious help to debug suspend to ram problem

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Message-ID: <20081006151140.GD1380@ucw.cz>
Date:	Mon, 6 Oct 2008 17:11:40 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Maxim Levitsky <maximlevitsky@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	linux-pm@...ts.linux-foundation.org,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: I need some serious help to debug suspend to ram problem

Hi!

>>> I hit a dead end when trying to understand why my notebook can't 
>>> resume from suspend to ram
>>> if this is done two times a row.
>>>
>>> Single suspend/resume cycle works almost perfectly (beep that goes 
>>> through the sound card is muted... no morse code for me... :-(
>>>
>>> )
>>>
>>> I compiled a minimal kernel (absolutely nothing but disk drivers, all experimental option like nohz
>>> turned off)
>>>
>>> But I had to turn SMP, since without it system won't resume first time I suspend it.
>>> (How could this affect suspend?)
>>
>> It could if the system is 64-bit.  In which case please have a look at
>> http://bugzilla.kernel.org/show_bug.cgi?id=11237
>>
>>> With SMP and minimal kernel (of course  no closed drivers), I get same behavior,
>>> first resume works second hangs.
>>>
>>> I then added some debug code to real mode wakeup code, I put there in first
>>> place instructions, that will save some magic value to rtc (to alarm
>>> registers that I know are preserved during boot cycle), and I 
>>> discovered   sad thing that first time bios does pass control to 
>>> linux, but second time
>>> (when it hangs), it doesn't. 
>>>
>>>
>>> I tried to update bios, and I got same results.
>>>
>>> Of course it does work with that @#$%^& OS
>>
>> So we're doing something wrong.  Please try the appended patch.
>>
>>> I then proceeded to test recently posted low memory corruption patch, and
>>> it did show that that @#$%^& BIOS does corrupt low memory I then 
>>> reserved all low memory, but system began to hand after first 
>>> suspend,
>>> in exactly same way, but as expected I soon discovered, that that forces real
>>> mode page to be above 1M, ok, then I reserved almost all low memory except
>>> 100K window in the middle, so low allocations will work, but be placed in
>>> region bios less likely to corrupt, and still that didn't help, still 
>>> same hang.    
>
> More information, I compiled kernels back to 2.6.19, and they all have exactly the same issue.
>

I must say you have done quite a lot of homework...

Ok, it looks like BIOS hangs before it can pass control to kernel. I
have seen it once before, and it was before we were using i8259 and
BIOS expected us to use ioapic (or vice-versa; its *long* time ago).

Good luck...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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