[v3,RFC] arm: use PSCI if available

Commit Message

Stefano Stabellini March 27, 2013, 5:10 p.m. UTC

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:

Comments

Rob Herring March 27, 2013, 5:45 p.m. UTC | #1

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

Arnd Bergmann March 27, 2013, 6:03 p.m. UTC | #2

On Wednesday 27 March 2013, Rob Herring wrote:
> 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);

The case that Stefano is interested in if obviously other platforms
that can either run as Dom0 under Xen with psci_smp_ops or natively
with their own smp_ops. A similar case would be a platform that
may implement psci using smc when run in secure mode but provide
its own smp_ops when run natively.

In both cases, it would be simpler to use psci if available but
fall back to mdesc->smp otherwise.

	Arnd

Stefano Stabellini March 27, 2013, 6:14 p.m. UTC | #3

On Wed, 27 Mar 2013, Arnd Bergmann wrote:
> On Wednesday 27 March 2013, Rob Herring wrote:
> > 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);
> 
> The case that Stefano is interested in if obviously other platforms
> that can either run as Dom0 under Xen with psci_smp_ops or natively
> with their own smp_ops. A similar case would be a platform that
> may implement psci using smc when run in secure mode but provide
> its own smp_ops when run natively.

That's correct.


> In both cases, it would be simpler to use psci if available but
> fall back to mdesc->smp otherwise.

I agree.

Patch

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