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From: Markus Armbruster <armbru@redhat.com>
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Date: Wed, 02 Mar 2016 16:50:30 +0100
In-Reply-To: <56D6F594.1010005@redhat.com> (Paolo Bonzini's message of "Wed, 2
	Mar 2016 15:15:48 +0100")
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Subject: Re: [Qemu-devel] [PATCH 18/38] ivshmem: Leave INTx alone when using
	MSI-X
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau <marcandre.lureau@gmail.com>, cam <cam@cs.ualberta.ca>, Claudio Fontana <claudio.fontana@huawei.com>, QEMU <qemu-devel@nongnu.org>, David Marchand <david.marchand@6wind.com>

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 02/03/2016 12:04, Markus Armbruster wrote:
>> For better or worse, fallback to INTx has never been implemented in
>> ivshmem.  You can either ask for an INTx-only device (msi=off), or for
>> an MSI-X-only device (msi=on).  The latter *cannot* do interrupts until
>> you enable MSI-X.
>
> Aha, now I see what you mean:
>
>     if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
>         msix_notify(pdev, vector);
>     } else {
>         ivshmem_IntrStatus_write(s, 1);
>     }
>
> So I believe your patch is okay.

I can try to explain it a bit better in the comment and/or commit
message when I respin.

>                                   Perhaps you could also change the
> interrupt pin for new machine types (even without changing the
> revision), but it's not necessary to do it.

I chose not to bother, because after PATCH 34, the non-deprecated
devices are all revision 1 (correct Interrupt Pin register).

>> Similarly, the ivshmem-doorbell device introduced later in this series
>> can only do MSI-X, and the ivshmem-plain device cannot do interrupts at
>> all.
>
> Here:
>
>     dev->config[PCI_INTERRUPT_PIN] = 0x01; /* interrupt pin 1 */

Ah!  I looked only for pci_config_set_interrupt_pin().