On Mon, 1 Apr 2013, Nicolas Pitre wrote: > On Mon, 1 Apr 2013, Stefano Stabellini wrote: > > > On Fri, 29 Mar 2013, Rob Herring wrote: > > > On 03/29/2013 12:53 PM, Nicolas Pitre wrote: > > > > On Fri, 29 Mar 2013, Stefano Stabellini wrote: > > > > > > > >> On Fri, 29 Mar 2013, Nicolas Pitre wrote: > > > >>> On Fri, 29 Mar 2013, Stefano Stabellini wrote: > > > >>> > > > >>>> If PSCI initializes correctly and PSCI SMP operations are available, > > > >>>> use them. > > > >>>> This is required for SMP support in Dom0 on Xen. > > > >>>> > > > >>>> Signed-off-by: Stefano Stabellini <stefano.stabell...@eu.citrix.com> > > > >>>> CC: will.dea...@arm.com > > > >>>> CC: a...@arndb.de > > > >>>> CC: marc.zyng...@arm.com > > > >>>> CC: li...@arm.linux.org.uk > > > >>>> CC: n...@linaro.org > > > >>> > > > >>> I'd suggest you also include in your series the patch I posted > > > >>> earlier > > > >>> providing a runtime mdesc->smp_init method as well. > > > >> > > > >> OK. > > > >> > > > >> > > > >>> This way the > > > >>> priority order would be: > > > >>> > > > >>> - If mdesc->smp_init is non null then use that. > > > >>> > > > >>> - Otherwise, if PSCI is available then use that. > > > >>> > > > >>> - Otherwise use mdesc->smp. > > > >>> > > > >>> This way, if the PSCI default has to be overriden (like in the MCPM > > > >>> case > > > >>> because it needs to wrap PSCI itself, or to cover Rob's concern) then > > > >>> this can be achieved at run time on a per mdesc basis. > > > >> > > > >> Actually that's not a bad idea, it could make everybody happy. > > > >> What about the following, in this precise order: > > > >> > > > >> - if a xen hypervisor node is present on device tree, use PSCI; > > > >> - otherwise if mdesc->smp_init is non null then use it; > > > >> - otherwise if PSCI is available then use it; > > > >> - otherwise use mdesc->smp. > > > >> > > > >> It's the most practical solution to satisfy everybody's needs. > > > > > > > > Maybe I'm missing something obvious, but why can't xen declare a mdesc > > > > of its own? Given it is going to tweak the DT passed to the kernel > > > > anyway that shouldn't be a problem. > > > > > > Xen does have it's own mdesc. It is (or will be) mach-virt, but that is > > > only for DomU guests. For Dom0, you still need all the platform specific > > > code except smp_ops. However, I'm doubtful this would work without other > > > changes on more complicated platforms like OMAP. > > > > > > I would say wait to add this until you have platforms that actually need > > > the first case. > > > > OK, that is not unreasonable. > > > > What are the platforms that are going to use smp_init? Do we know how do > > they intend to use it? > > VExpress for one. When booting on a big.LITTLE system such as TC2 on > VExpress, the MCPM layer needs to arbitrate power management operations > on a per cluster basis. In that case there is a MCPM specific set of > SMP ops to be used, even if it may end up calling into PSCI. > > But the important point is that we don't know beforehand what to use, > especially with a kernel that can boot on multiple different VExpress > configurations. The decision has to be made at run time, and therefore > a static default or mdesc->smp ops doesn't cut it.
I certainly like the principle and I am in favor of anything that moves the decisions at runtime. I have pulled the patch in the series, it's going to be in the next version. However I am concerned that these platform specific operations won't work with Xen at all. I am getting increasingly certain that we need a Xen specific check in setup_arch to bump up of the priority of PSCI over anything else if Xen is running. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
