Messages in this thread | | | Date | Fri, 5 Apr 2013 20:15:51 -0400 (EDT) | From | Nicolas Pitre <> | Subject | Re: [PATCH v6 4/4] xen/arm: introduce xen_early_init, use PSCI on xen |
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On Sat, 6 Apr 2013, Stefano Stabellini wrote:
> On Fri, 5 Apr 2013, Nicolas Pitre wrote: > > On Fri, 5 Apr 2013, Rob Herring wrote: > > > > > On 04/05/2013 02:36 PM, Nicolas Pitre wrote: > > > > On Fri, 5 Apr 2013, Stefano Stabellini wrote: > > > > > > > >> This is what happens: > > > >> > > > >> - No Xen > > > >> Xen is not running on the platform and a Xen hypervisor node is not > > > >> available on device tree. > > > >> Everything keeps working seamlessly, this patch doesn't change anything. > > > >> > > > >> - we are running on Xen > > > >> Xen is running on the platform, we are running as a guest on Xen and an > > > >> hypervisor node is available on device tree. > > > >> Let's also assume that there aren't any "arm,cci" compatible nodes on > > > >> device tree because Xen wouldn't export this kind of information to any > > > >> guests right now. Therefore PSCI should be used to boot secondary cpus. > > > >> Because the versatile express machine sets smp_init to > > > >> vexpress_smp_init_ops, vexpress_smp_init_ops will be called. > > > >> vexpress_smp_init_ops sets smp_ops to vexpress_smp_ops, that *break* > > > >> Xen. > > > > > > > > OK I see. > > > > > > > >> With this patch, xen_smp_init will be called instead of > > > >> vexpress_smp_init_ops, and smp_ops will be set to psci_smp_ops, > > > >> therefore *unbreaking* Xen. > > > > > > > > However that breaks MCPM. > > > > > > You mean on bare metal, right? For the bare metal, "xen,xen" property > > > would not be present and xen_smp_init is not used. So the vexpress MCPM > > > ops will be used. Aren't Dom0 cpu's basically virtual cpus? If Xen ever > > > needs the MCPM support, the Xen hook itself can figure out whether to > > > use MCPM support. > > > > Well, if Xen has its own mdesc distinct from the VExpress one then > > things > > are indeed fine. > > It's not about the mdesc: Xen has its own hypervisor node on device tree > if and only if Xen is running on the platform, therefore the Xen early > hook is never going to do anything at all on native. > > In other words, this patch should NOT change the behaviour of Linux on > native, and if it did, it would be a bug.
Perfect.
Nicolas
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