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

From: Jan Kiszka
Subject: Re: [Qemu-devel] [PATCH 06/13] pci: Add INTx routing notifier
Date: Sun, 10 Jun 2012 14:33:03 +0200
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On 2012-06-10 14:16, Michael S. Tsirkin wrote:
> 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.

True. OK, I can do the recursion in pci_bus_fire_intx_routing_notifier
directly instead of pushing this into the bridge.

>>> 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.

This wouldn't change the picture very much: Before the host bridge is
fully initialized, there is no valid route available. But before that,
there is also no device attached to it. So the invocation pattern
wouldn't change.

What would change is the semantic of the interface to the host bridge.
So what about this: provide a public pci_root_bus_intx_routing_updated
which so far just calls the internal-use-only


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