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

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Message-ID: <51533037.5060004@gmail.com>
Date:	Wed, 27 Mar 2013 12:45:27 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	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 03/27/2013 12:10 PM, 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:
> 
> 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);

No, I was thinking in the case of Xen and mach-virt, you would not set
mdesc->smp. So you would have something like this:

if (mdesc->smp)
	smp_set_ops(mdesc->smp);
else
	smp_set_ops(&psci_smp_ops);


Rob

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