Re: [Xen-devel] [PATCH v2 6/6] [RFC] arm: use PSCI if available

[Arnd Bergmann <arnd@xxxxxxxx>]

On Tuesday 26 March 2013, Will Deacon wrote:
> > They can even base the implementation of their smp_ops on the current
> > psci code, in order to facilitate that I could get rid of psci_ops
> > (which initialization is based on device tree) and export the psci_cpu_*
> > functions instead, so that they can be called directly by other smp_ops.
> 
> Again, I think this destroys the layering. The whole point is that the PSCI
> functions are called from within something that understands precisely how to
> talk to the firmware and what it is capable of.

Right, we probably the psci smp ops to be separate from the rest of the psci
code, but I also think that Stefano is right that we should let any platform
use the psci smp ops if possible, rather than having to implement their own.

> > > If this can indeed work for the virtual platforms (Xen and KVM), then I
> > > think it would be better expressed using `virt' smp_ops, which map 
> > > directly
> > > to PSCI, rather than putting them here. Even then, it's tying KVM and Xen
> > > together on the firmware side of things...
> > 
> > Keep in mind that dom0 on Xen boots as a native machine (versatile
> > express or exynos5 for example) with a Xen hypervisor node on it.  We
> > would need to find a way to override the default machine smp_ops with
> > a set of xen_smp_ops early at boot.
> > I don't like this option very much, I think is fragile.
> 
> Why can't dom0 use whatever smp ops the native machine would use?

The part that I'm most interested in is making it possible for a platform
to kill off its native smp ops in the kernel by implementing the psci
ops. I think it's a good strategy to use psci by default if both 
platform and psci implementations are available.

        Arnd

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