[PATCH 8/8] ARM: vexpress/dcscb: select multi-cluster SMP operations

[Nicolas Pitre]

On Wed, 29 May 2013, Jon Medhurst (Tixy) wrote:

> On Fri, 2013-05-24 at 01:45 -0400, Nicolas Pitre wrote:
> > When the DCSCB code is successfully probed and initialized, then the
> > generic MCPM SPM ops should be used as those operations need to be
> > arbitrated through the MCPM layer.
> > 
> > Signed-off-by: Nicolas Pitre <nicolas.pitre at linaro.org>
> > ---
> >  arch/arm/mach-vexpress/dcscb.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/arch/arm/mach-vexpress/dcscb.c b/arch/arm/mach-vexpress/dcscb.c
> > index 1acc975360..ce3118dc05 100644
> > --- a/arch/arm/mach-vexpress/dcscb.c
> > +++ b/arch/arm/mach-vexpress/dcscb.c
> > @@ -239,6 +239,8 @@ static int __init dcscb_init(void)
> >  		return ret;
> >  	}
> >  
> > +	mcpm_smp_set_ops();
> > +
> 
> This is going to change the platform's smp_ops after setup_arch() has
> already set them, is that OK and not too late?

Well...  The only methods being invoked before the booting of secondary 
CPUs are smp_init_cpus and smp_prepare_cpus.  In the MCPM case they're 
both no-ops.

> I ask, because for me, RTSM doesn't boot the secondary CPUs if we rely
> on this change to set the smp_ops, but having a hook in setup_arch() to
> select instead of the standard vexpress ops does work.

Strange.  That works for me both ways.

I did it this way because the alternative probe for a CCI in unrelated 
code in order to install the MCPM ops and this really looks awkward.  
And it won't work if for example PSCI mode decides not to let Linux see 
the CCI.

Is there something in the default vexpress smp_init_cpus and 
smp_prepare_cpus code that could prevent booting through MCPM later on?


Nicolas