linux-kernel - Re: [PATCH v3] [RFC] arm: use PSCI if available

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Date:	Wed, 27 Mar 2013 13:24:51 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
cc:	Rob Herring <robherring2@...il.com>,
	Will Deacon <will.deacon@....com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"arnd@...db.de" <arnd@...db.de>,
	Marc Zyngier <Marc.Zyngier@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3] [RFC] arm: use PSCI if available

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@...aro.org>
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@...aro.org>
Signed-off-by: Nicolas Pitre <nicolas.pitre@...aro.org>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@...com>

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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