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

[Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>]

On Wed, 27 Mar 2013, Stefano Stabellini wrote:

> 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:
[...]

What about the patch below that I'm carying in my MCPM branch 
which has been posted here already:

From: Jon Medhurst <tixy@xxxxxxxxxx>
Date: Thu, 13 Dec 2012 13:23:13 +0000
Subject: [PATCH] ARM: Enable selection of SMP operations at boot time

Add a new 'smp_init' hook to machine_desc so platforms can specify a
function to be used to setup smp ops instead of having a statically
defined value.

Signed-off-by: Jon Medhurst <tixy@xxxxxxxxxx>
Signed-off-by: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@xxxxxx>

diff --git a/arch/arm/include/asm/mach/arch.h b/arch/arm/include/asm/mach/arch.h
index 308ad7d6f9..c01bf53b85 100644
--- a/arch/arm/include/asm/mach/arch.h
+++ b/arch/arm/include/asm/mach/arch.h
@@ -16,8 +16,10 @@ struct pt_regs;
 struct smp_operations;
 #ifdef CONFIG_SMP
 #define smp_ops(ops) (&(ops))
+#define smp_init_ops(ops) (&(ops))
 #else
 #define smp_ops(ops) (struct smp_operations *)NULL
+#define smp_init_ops(ops) (void (*)(void))NULL
 #endif
 
 struct machine_desc {
@@ -41,6 +43,7 @@ struct machine_desc {
        unsigned char           reserve_lp2 :1; /* never has lp2        */
        char                    restart_mode;   /* default restart mode */
        struct smp_operations   *smp;           /* SMP operations       */
+       void                    (*smp_init)(void);
        void                    (*fixup)(struct tag *, char **,
                                         struct meminfo *);
        void                    (*reserve)(void);/* reserve mem blocks  */
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 3f6cbb2e3e..41edca8582 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -768,7 +768,10 @@ void __init setup_arch(char **cmdline_p)
        arm_dt_init_cpu_maps();
 #ifdef CONFIG_SMP
        if (is_smp()) {
-               smp_set_ops(mdesc->smp);
+               if(mdesc->smp_init)
+                       (*mdesc->smp_init)();
+               else
+                       smp_set_ops(mdesc->smp);
                smp_init_cpus();
        }
 #endif

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