Re: [PATCH v5.99.1 RFC 1/4] xen/arm: Duplicate gic-v2.c file to support hip04 platform version

[Ian Campbell <ian.campbell@citrix.com>]

On Wed, 2015-02-25 at 16:34 +0000, Stefano Stabellini wrote:
> I am concerned about the increased size of the Xen binary as a result of
> the introduction of this driver.

I'm also somewhat concerned about the ongoing maintenance of a
proliferation of (subtly or otherwise) different interrupt controllers.
(I remember too well the morass which Linux/ARM was in a few years ago
with all the h/w variations, which they have spent many years getting on
top of.)

Speaking only for myself I am (obviously) happy to be part of the
maintenance effort for the architecturally defined(/compliant, whatever)
ones and of the generic infrastructure.

But I think it is reasonable to expect the interested community members
to pick up the burden for anything else they would like to add, rather
than expecting the core maintainers to do it. (which BTW implies this
patch should include a hunk touching MAINTAINERS)

I also think it would be reasonable for us to drop support for hardware
which is not being adequately maintained. (Not that I expect that to
happen here, but it is inevitable that eventually we will see such
drivers I think). "adequately maintained" would mean things like timely
responses to core infrastructure updates and not bit-rotting.

> I think we should disable the build of all drivers in Xen by default,
> except for the ARM standard compliant ones (for aarch64 the SBSA is a
> nice summary of what is considered compliant), to keep the size of the
> binary small.

I don't think the SBSA is necessarily the best reference here, since it
only defines what is standardised within the scope of "server
systems" (whatever you take that to mean) and there are things which do
not fall under that umbrella.

That said I'm not sure what better reference there is.

Maybe even on non-server systems the set of hardware which Xen has to
drive itself is limited to things which are covered by the SBSA in
practice, by the nature of the fact that the majority of the wacky stuff
is driven from hardware domains.

So maybe SBSA is OK then...

> Could you please introduce a Xen build time option in
> xen/arch/arm/Rules.mk, called HAS_NON_STANDARD_DRIVERS, that by default
> is n, and gate the build of gic-hip04.c on it?

I'm rather wary of creating a "two tier" system like this, but I cannot
think of a better compromise :-(

Ian.