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Date: Tue, 16 Jun 2009 20:12:26 +0300
Message-ID: <f43fc5580906161012h37b33d3fje5d802fc638a217b@mail.gmail.com>
Subject: Re: [Qemu-devel] Register uhci_reset() callback.
From: Blue Swirl <blauwirbel@gmail.com>
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To: Paul Brook <paul@codesourcery.com>
Cc: qemu-devel@nongnu.org, Gleb Natapov <gleb@redhat.com>, Avi Kivity <avi@redhat.com>

On 6/16/09, Paul Brook <paul@codesourcery.com> wrote:
> On Tuesday 16 June 2009, Gleb Natapov wrote:
>  > On Tue, Jun 16, 2009 at 06:14:51PM +0300, Blue Swirl wrote:
>  > > > Because interrupt line is stuck a guest can't get to the point where it
>  > > >  loads a driver to the second device. For outside observer the guest
>  > > >  just hangs.
>  > >
>  > > I see. The problem is in piix_pci interrupt handling, pci_irq_levels[]
>  > > should be set to zero on reset.
>  >
>  > The patch that does that was rejected earlier :)
>  > http://lists.gnu.org/archive/html/qemu-devel/2009-06/msg00342.html
>  > http://lists.gnu.org/archive/html/qemu-devel/2009-06/msg00344.html
>
>
> You're both wrong.
>
>  If allow devices to be reset independently then they should probably set theit
>  IRQ output on reset.
>
>  IRQ muxes (e.g. PCI busses) should handle reseting and save/restore of their
>  own internal state.

Fully agree.

>  Devices should not cause IRQ state changes on restore. Commit 3dcd219f is
>  incorrect.

I'm not so sure about this, but I can't think of a restore sequence
where the IRQ state would need to be changed if the IRQs tied together
are handled correctly. But surely if the devices states are restored
in strange order, the state changes could cause problems because the
device receiving the IRQ may still contain old state.