Re: RFC: add MSI/MSI-X support to NetBSD

[Matt Thomas <matt%3am-software.com@localhost>]

On Jun 6, 2014, at 12:06 PM, Taylor R Campbell 
<campbell+netbsd-tech-kern%mumble.net@localhost> wrote:

>   Date: Fri, 6 Jun 2014 12:56:53 -0500
>   From: David Young <dyoung%pobox.com@localhost>
> 
>   Here is the proposal that I came up with many months (a few years?) ago
>   with input from Matt Thomas.  I have tried to account for Matt's
>   requirements, but I'm not sure that I have done so.
> 
> For those ignoramuses among us who remain perplexed by the apparent
> difficulty of using a new interrupt delivery mechanism, could you add
> some notes to your proposal about what driver authors would need to
> know about it and when & how one would use it in a driver?
> 
> Would all architectures with PCI support bus_msi(9), or would PCI
> device drivers need to conditionally use it?  Why isn't it just a
> matter of modifying pci_intr_map, or calling pci_intr_map_msi like in
> OpenBSD?  Would there be other non-PCI buses with message-signalled
> interrupts too?

Those that support PCIe or PCIX and support MSIs should change.  But
we can continue the legacy INT[A-D].  For performance, MSIs should
be more efficient.

> (Still not having done my homework to study what this MSI business is
> all about, I'll note parenthetically that it seems FreeBSD and OpenBSD
> have supported MSI for a while, and I understand neither why it was so
> easy for them nor what advantage they lack by not having bus_msi(9).)