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

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   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?

(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).)