Re: In kernel PIC support: kernel patch

Luca
2007-06-27T15:50:59Z

On 6/26/07, Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org> wrote:
> On Mon, 2007-06-25 at 18:08 -0400, Avi Kivity wrote:
> > > Note that there is another standard that would allow us to use built-in
> > > routing without ACPI/IOAPIC: MSI. I know the battle over
> > > virtual-bus-rendering is still raging w.r.t. to PCI or not-PCI. But I
> > > will point out that if we do use PCI, setting the PV devices up as MSI
> > > capable in the config space potentially eliminates the need to also wire
> > > them to an IOAPIC. They will get their vector data from the MSI setup
> > > and can then send APIC messages directly. (I think there is some
> > > confusion about how we can do MSI later in this thread...I will reply to
> > > those mails separately)
> > >
> >
> > MSI is also a good solution; but do all semi-modern guest OSes support it?
>
> I can't say for sure, but I would guess "yes" because IIUC PCI-Express
> only uses MSI (or at least heavily prefers it).

AFAIK for PCI-E devices MSI support is mandated by the standard. OTHO
there's also the INTx emulation (the device *always* uses a write
transaction to signal the interrupt condition, and the host bridge may
turn the message into a legacy interrupt) so that the OS can drive the
device even without fiddling with MSI.
As Eddie said XP probably would be confused by MSI-only devices.

Luca