[Ksummit-2012-discuss] PCI breakout session

Benjamin Herrenschmidt benh at kernel.crashing.org
Sun Jun 17 21:42:51 UTC 2012


(snip general approval)

So folks, what should be the format ? Do we organize a mini-summit
proper with an agenda or we just breakout during KS itself ?

Ted, does the venue has facilities for us to do something maybe the day
before ? Or we just do it informally in the corridors ? :-)

I think the main thing to discuss is rework & cleanup of hotplug which
is a large impact (PCI boot code as well) if we want to do it properly,
which means having essentially the same code path overall to deal with
normal PCI probe and hotplug.

The main issue I see in term of infrastructure is how we rely on
initcall "levels" and ordering of things at boot to do things like
probe, then assign resources, then fixups, then bind drivers. It's
fragile and doesn't work properly with hotplug, meaning that hotplug
uses a subtely different ordering (and totally fails to call the final
fixups).

The "right" approach is to probably move the resource assignment to
between the initial scan pass and the "adding" of devices (in our PCI
stack terminology, adding -> register with the driver model), and
naturally have the final fixups called right before the latter. But this
will have some sort of impact on all archs so we probably want to do
quite a bit of code auditing first.

Of course that's scary since PCI is so prone to regressions, especially
on x86 ...

I have some specific issues with resource allocation on bridges that
segment the MMIO space in interesting ways (for error handling) that I
want to discuss and get feedback on how to best deal with.

Do we start writing an agenda ?

Cheers,
Ben.






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