Re: [PATCH v2 1/2] ARM: Availability of psci_smp_available depends on CONFIG_SMP

[Thierry Reding <treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

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On Tue, Oct 06, 2015 at 04:18:58PM +0100, Will Deacon wrote:
> On Tue, Oct 06, 2015 at 10:11:24AM +0200, Thierry Reding wrote:
> > On Wed, Sep 23, 2015 at 08:39:43AM +0200, Jan Kiszka wrote:
> > > Ensure that we can use psci_smp_available without checking for
> > > CONFIG_SMP first.
> > > 
> > > Signed-off-by: Jan Kiszka <jan.kiszka-kv7WeFo6aLtBDgjK7y7TUQ@public.gmane.org>
> > > ---
> > >  arch/arm/include/asm/psci.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm/include/asm/psci.h b/arch/arm/include/asm/psci.h
> > > index 68ee3ce..ff956f4 100644
> > > --- a/arch/arm/include/asm/psci.h
> > > +++ b/arch/arm/include/asm/psci.h
> > > @@ -16,7 +16,7 @@
> > >  
> > >  extern struct smp_operations psci_smp_ops;
> > >  
> > > -#ifdef CONFIG_ARM_PSCI
> > > +#if defined(CONFIG_ARM_PSCI) && defined(CONFIG_SMP)
> > >  bool psci_smp_available(void);
> > >  #else
> > >  static inline bool psci_smp_available(void) { return false; }
> > 
> > Hi Will,
> 
> Hi Thierry,
> 
> > you had questions about this when this was first submitted back in
> > May[0], but discussion stalled. Can you take another look, please?
> > 
> > I think irrespective of what the series is trying to do this is a
> > correct fix. The arch/arm/kernel/psci_smp.c file is only compiled if
> > both ARM_PSCI and SMP are selected. Builds break if we don't mirror
> > that conditional in the header because for ARM_PSCI && !SMP no dummy
> > will be defined, but the implementation for the prototype won't be
> > available either, leading to a linker error.
> 
> Sure, I'm fine with this patch in isolation, I just didn't (don't) fully
> grok what the series is trying to achieve.

The goal is to prevent the kernel from registering a CPU idle driver if
PSCI is going to be used for SMP. This is necessary because both the CPU
idle driver and the PSCI implementation (provided by U-Boot in this
case) access the same resources. The effect of having both enabled is
usually that the system will simply hang sometime during boot.

Thierry

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