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Re: [qemu-s390x] [PATCH v3 03/19] xics: Disintricate allocation and type

From: David Gibson
Subject: Re: [qemu-s390x] [PATCH v3 03/19] xics: Disintricate allocation and type setting of interrupts
Date: Wed, 6 Feb 2019 12:47:55 +1100
User-agent: Mutt/1.10.1 (2018-07-13)

On Tue, Feb 05, 2019 at 03:59:15PM +0100, Greg Kurz wrote:
> On Tue, 5 Feb 2019 17:13:46 +1100
> David Gibson <address@hidden> wrote:
> > On Thu, Jan 17, 2019 at 06:14:46PM +0100, Greg Kurz wrote:
> > > The current code assumes that an interrupt is allocated as soon as its
> > > type is set to MSI or LSI. PHB hotplug will require to be able to set
> > > the type of an interrupt before actually allocating it.  
> > 
> > Hm.. why?
> > 
> The justification for that is given in patch 6 actually:
> Every PHB needs to claim 4 LSIs to support legacy PCI devices. This is
> currently done at PHB realize. When using in-kernel XICS (or upcoming
> in-kernel XIVE), QEMU synchronizes the state of all irqs, including
> these LSIs, later on at machine reset.
> In order to support PHB hotplug, we need a way to tell KVM about the
> LSIs that doesn't require a machine reset. Since these irq numbers are
> fixed values derived from the PHB index, let's identify them all at
> machine init. Older machines that don't have fixed irq numbers cannot
> support PHB hotplug and keep the existing behavior.

Sounds good.

> FYI, I'm currently reworking that part entirely. Maybe not worth wasting to
> much time on reviewing this v3.

Ok, I have plenty of other stuff to review, so I'll wait for the next spin.

David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!

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