As for supporting multiple irqs in plain MSI mode, I don't think
we want to do that. The problem is that multiple interrupts
in msi mode cannot be individually routed.
On some(/many/most) platforms that isn't a problem. Platforms
for which it is can just refuse to allocate more than one MSI
at once.
I think we really want
to encourage vendors who are building cards with multiple MSI irqs
to use MSI-X. MSI-X has a lot fewer ugly special cases and all
architectures can individually route the irqs.
We still should support whatever hardware already exists, if
possible.
If there are interesting cards that support just MSI mode and really
need more than one irq I would be happy to reconsider that decision
but my impression was that plain MSI was basically not quite flexible
enough to really be interesting, and supporting just one MSI irq was
ok but any more would lead to all kinds of strange special cases.
Individual drivers can deal with those special cases if they are device-
specific; and the platform can just refuse to do more than one MSI if
something platform-specific would prevent correct operation.
It would be nice to have the MSI and MSI-X interfaces have the same
calling convention; in fact, they can probably be folded into one.
Segher
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