[Xen-devel] Re: [PATCH 07/12] xen: events: separate MSI PIRQ allocation from PIRQ binding to IRQ

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Mon, 2011-02-21 at 12:50 +0000, Stefano Stabellini wrote:
> On Fri, 18 Feb 2011, Ian Campbell wrote:

> my only concern is about the order of the calls: on native and on xen
> before this patch the order is
> 
> msi_compose_msg
> set_irq_msi
> write_msi_msg
> 
> while after this patch the order is:
> 
> msi_compose_msg
> write_msi_msg
> set_irq_msi
> 
> however I don't think it makes a difference because msi (and msix)
> are not enabled yet anyway on the pci device in question (they are
> enabled by msi(x)_capability_init right after calling
> arch_setup_msi_irqs).

My take is that write_msi_msg is literally get_irq_msi (to fetch the
corresponding struct msi_desc) followed by __write_msi_msg. The
set_irq_msi does nothing other than associate an msi_desc with an IRQ
number in order that the get_irq_msi can return it.

But since we have the right msi_desc in our hand already using
__write_msi_msg directly is OK and so this ordering is fine.

Ian.


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