Subject: [PATCH 1/6] ARM: Add inline function smp_on_up() for early init testing

From: [email-masked] (Tony Lindgren)
Date: Thu, 2 Sep 2010 10:42:44 -0700

* Russell King - ARM Linux <[email-masked]> [100902 10:00]:
> On Thu, Sep 02, 2010 at 09:18:47AM -0700, Tony Lindgren wrote:
> 
> > --- a/arch/arm/include/asm/smp_plat.h
> > +++ b/arch/arm/include/asm/smp_plat.h
> > @@ -39,4 +39,20 @@ static inline int cache_ops_need_broadcast(void)
> >  #define UP(instr...)	_str(instr)
> >  #endif
> >  
> > +static inline int smp_on_up(void)
> > +{
> > +#ifdef CONFIG_SMP_ON_UP
> > +	int smp_on_up;
> > +
> > +	asm(							\
> > +		SMP(mov	%0, #0)					\
> > +		UP(mov	%0, #1)					\
> > +		: "=r" (smp_on_up));
> > +
> > +	return smp_on_up;
> > +#else
> > +	return 0;
> > +#endif
> 
> I think this is the wrong approach - rather than a function which tells us
> just if we are a SMP kernel running on UP, why not something which returns
> whether we're running on SMP and use that to eliminate some of these ifdefs?

Sure. Will has something like this in his patches:

static inline int cpu_is_part_of_mp_system(void)
{
	u32 mpidr;
	asm volatile("mrc p15, 0, %0, c0, c0, 5" : "=r" (mpidr));
	return (mpidr >> 31) ? !(mpidr >> 30) : 0;
}

BTW, so far looks like we should only need this during init to set up things.

Regards,

Tony