Re: [PATCH 2/2] Initial generic hypertransport interrupt support.

[Segher Boessenkool <segher@kernel.crashing.org>]

> 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