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Re: [Qemu-devel] [PATCH 11/22] i8259: Update IRQ state after reset

From: Blue Swirl
Subject: Re: [Qemu-devel] [PATCH 11/22] i8259: Update IRQ state after reset
Date: Fri, 30 Sep 2011 20:52:23 +0000

On Fri, Sep 30, 2011 at 9:14 AM, Peter Maydell <address@hidden> wrote:
> On 30 September 2011 07:47, Jan Kiszka <address@hidden> wrote:
>> There is no difference between system reset after power-up or later on.
>> And there should be no difference between per device, per group of
>> devices or system-wide reset. A device model cannot tell these apart.
> I think it's also useful to distinguish "system reset" meaning 'simulated
> reset button was pressed, causing the reset line to be asserted on various
> devices' from "simulation reset" meaning 'qemu effectively tore down the
> whole simulation and put it into the same state it would be when qemu
> initially starts'. I don't think you can usefully reset a single device
> except by asserting its simulated reset signal, except possibly for
> hotplug type situations where you're simulating applying power to it.

In the 2009 thread, i286 triple fault was mentioned. It's also
possible to reset a single device, which can then reset a slave device
and so forth, like Sparc32 DMA controller can reset ESP device and
that should perform a SCSI bus reset.

>> My series does not depend on this cleanup/fix, but the reason not to
>> apply remains wrong IMHO.
> (just to be clear) I'm not arguing against your patch, just more
> generally that I'm not sure our current model of reset is entirely
> coherent.
> -- PMM

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