Re: [Ksummit-discuss] [TECH TOPIC] Addressing complex dependencies and semantics (v2)

["Jörg Rödel" <jroedel@suse.de>]

On Mon, Aug 01, 2016 at 09:03:09PM +0200, Luis R. Rodriguez wrote:
> Another piece of code that deals with complex dependencies I've recently
> ventured into was the x86 IOMMU stuff. The complexities here are both at
> the built-in init level and also later at probe.

Yeah, everything is fine when both, AMD-KFD and the IOMMUv2 driver are
built as modules, as the order of loading these modules is
preserved by symbol dependencies. But when they are built-in these
modules also need to be initialized in the right order, otherwise the
KFD-driver will call into an uninialized IOMMU driver and crashes the
system. Long-term this will be fixed by always build-in the IOMMU-parts
(when they are merged with the Intel-SVM support), but in general not
being able to express dependencies between build-in modules remains to
be a problem.

I have spent spent some thoughts on how this could be solved, and one
idea I had was to rework the way build-in modules work. If they are not
linked into the kernel at compile-time, but at boot-time, this problem
would be solved. On the other hand this slows down boot (is this important
when distro-kernels build everything as modules anyway?) and probably
doesn't solve the dependency problems for power-management or elsewhere
in kernel.

So I'd like to participate if this is going to be discussed.


Thanks,

	Joerg