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Date: Fri, 31 May 2013 14:48:27 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v7 1/4] isapc: Fix non-KVM qemu boot
 (read/write memory for isapc BIOS)
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To: Laszlo Ersek <lersek@redhat.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>, Kevin O'Connor <kevin@koconnor.net>, Jordan Justen <jljusten@gmail.com>, David Woodhouse <dwmw2@infradead.org>, qemu-devel <qemu-devel@nongnu.org>

Il 31/05/2013 14:40, Laszlo Ersek ha scritto:
> I think we've been here before...
> 
> - always resetting the PAM registers broke S3 resume:
> http://thread.gmane.org/gmane.comp.emulators.qemu/195931/focus=195932
> http://thread.gmane.org/gmane.comp.emulators.qemu/195931/focus=196081
> 
> - there was a patch to distinguish soft reset from hard reset:
> http://thread.gmane.org/gmane.comp.emulators.qemu/195351

This is still planned, but it won't touch the PAM registers so as not to
break S3.  Peter Stuge said that the memory controller registers keep
their content across S3 in real machines too.

> - another approach for soft vs. hard, and how it relates to resume:
> http://thread.gmane.org/gmane.comp.emulators.qemu/198545/focus=198546
> 
> I believe currently qemu doesn't distinguish soft from hard reset. Hard
> reset would have to reset PAM registers, soft reset must not.

Hard reset = powerdown, soft reset = reset or S3.

QEMU only cares about soft reset.  There is one case where that matters,
which is "-no-shutdown -no-reboot".  Here you can go to S4 or S5 and
then type "cont", and the machine will behave as if you actually did a
soft reset.  I don't think it matters much in practice, though.

Paolo