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

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Message-ID: <alpine.DEB.2.02.1303271753130.4430@kaball.uk.xensource.com>
Date:	Wed, 27 Mar 2013 18:22:15 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	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, Nicolas Pitre wrote:
> 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:

It's a step in the right direction but it still wouldn't solve the
problem.
Let me describe the scenario again:

- we have a versatile express machine with Xen running on it (or an
  exynos5, etc.);
- Xen boots Linux as Dom0, passing a versatile express device tree with
  the Xen hypervisor node added to it;
- Linux is booting, using the versatile express device tree for hardware
  discovery;
- Linux can access the hardware described in the device tree because Xen
  remapped the MMIO regions appropriately;
- Linux needs to bring secondary cpus up, but Xen only exports a PSCI
  interface, so the native versatile express smp_ops don't work;
- Linux needs to detect that PSCI is available (or Xen is available with
  its set of xen_smp_ops) and preferable on this platform and uses it
  instead of the versatile express smp_ops.



> 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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