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Re: [Qemu-devel] [PATCH 06/13] pci: Add INTx routing notifier

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH 06/13] pci: Add INTx routing notifier
Date: Sun, 10 Jun 2012 15:16:29 +0300

On Sun, Jun 10, 2012 at 02:09:20PM +0200, Jan Kiszka wrote:
> On 2012-06-10 13:39, Michael S. Tsirkin wrote:
> > It's OK to use recursion but when done through a callback
> > like this it's unreadable.
> Isn't the alternative poking into foreign bridge device states for their
> secondary buses?

pci_set_bus_intx_routing does this already.

> > Also, you need to setup you cache after intx cache has been
> > initialized, and you provide no clean way to do that.
> Once a PCI device is registered, the INTx route can be queried. So the
> device user will call pci_device_route_intx_to_irq once (e.g. in the
> device init function which is invoked afterward) to fill its cache and
> receive a notification if an update is needed. I do not see why, and
> specifically how you could query the route earlier or register a callback.

Before pci_bus_irqs is called.
Why is another question.

> > 
> > One way to fix all this is call the notifier for devices, if set, from
> > pci_set_bus_intx_routing.
> > Then assume that intx to irq translations can be cached
> > even though they aren't now. So you will need to invoke
> > pci_set_bus_intx_routing on intx to irq mapping changes,
> > and that fires the notifier for free.
> pci_set_bus_intx_routing is really only for the initial setup of the
> static INTx pin routes. And this happens on
> pci_bus_irqs/pci_register_bus, ie. triggered by the host bridge. By that
> time, there can't be any notifier listeners - as there are no devices yet.
> Jan

What I am saying is we'll cache the final IRQ at some point.
Pretend it's already that way so callers are ready for this.


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