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SubjectRe: I need some serious help to debug suspend to ram problem

>>> 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
>>> 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...
(cesky, pictures)

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