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

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Message-ID: <alpine.DEB.2.02.1303271642340.4430@kaball.uk.xensource.com>
Date:	Wed, 27 Mar 2013 17:10:26 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Rob Herring <robherring2@...il.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.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>,
	"nico@...aro.org" <nico@...aro.org>,
	"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, 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)
 	unflatten_device_tree();
 
 	arm_dt_init_cpu_maps();
+	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);
 		smp_init_cpus();
 	}
 #endif
--
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