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Re: [Xen-devel] [PATCH v3] [RFC] arm: use PSCI if available

On Wed, 27 Mar 2013, Rob Herring wrote:
> On 03/27/2013 11:23 AM, Stefano Stabellini wrote:
> > Would you agree on a patch that moves virt_smp_ops out of mach-virt and
> > renames them to psci_smp_ops (maybe to arch/arm/kernel/psci_smp_ops.c)?
> > 
> > Would you agree on initializing psci from setup_arch, right after the
> > call to arm_dt_init_cpu_maps()?
> > 
> > Finally the most controversial point: would you agree on using
> > psci_smp_ops by default if they are available?
> > If not, would you at least agree on letting Xen overwrite the default
> > machine smp_ops?
> > We need one or the other for dom0 support.
> It should not be *always* use PSCI smp ops if available, but use them
> only if the platform does not define its own smp ops.

Well, that is the one additional problem that we have on Xen.

On x86 Xen replaces a lot of core native function calls with its own
implementations (see paravirt_ops).
On ARM we only need *one* set of calls: the smp_ops calls.

So if we don't want to give priority to PSCI over the platform smp_ops,
then we need a simple workaround just for Xen in common code like the
one appended below.
Not pretty, but at least small:

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 3f6cbb2..08cf7e0 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -43,6 +43,8 @@
 #include <asm/cacheflush.h>
 #include <asm/cachetype.h>
 #include <asm/tlbflush.h>
+#include <xen/xen.h>
+#include <asm/xen/hypervisor.h>
 #include <asm/prom.h>
 #include <asm/mach/arch.h>
@@ -766,9 +768,13 @@ void __init setup_arch(char **cmdline_p)
+       xen_early_init();
 #ifdef CONFIG_SMP
        if (is_smp()) {
-               smp_set_ops(mdesc->smp);
+               if (xen_domain())
+                       smp_set_ops(&xen_smp_ops);
+               else
+                       smp_set_ops(mdesc->smp);

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