Subject: Re: [RFC PATCH 14/17] powerpc/book3e-64/kexec: Enable SMP release

From: Scott Wood <[email-masked]>
Date: Mon, 24 Aug 2015 15:25:48 -0500

On Thu, 2015-08-20 at 14:54 +1000, Michael Ellerman wrote:
> Hi Scott,
> 
> Sorry for the delay. So I'm back to square one on this patch.
> 
> On Sat, 2015-07-18 at 15:08 -0500, Scott Wood wrote:
> > booted_from_exec is similar to __run_at_load, except that it is set for
> > regular kexec as well as kdump.
> > 
> > The flag is needed because the SMP release mechanism for FSL book3e is
> > different from when booting with normal hardware.  In theory we could
> > simulate the normal spin table mechanism, but not at the addresses
> > U-Boot put in the device tree -- so there'd need to be even more
> > communication between the kernel and kexec to set that up.  Since
> > there's already a similar flag being set (for kdump only), this seemed
> > like a reasonable approach.
> 
> Although this is a reasonable approach, I don't think it's the best 
> approach.
> 
> AFAICS there's no reason why we can't use a device tree property for this, 
> so I
> think we should do that.

OK, I'll look into that.

> 
> > diff --git a/arch/powerpc/platforms/85xx/smp.c 
> > b/arch/powerpc/platforms/85xx/smp.c
> > index 5152289..4abda43 100644
> > --- a/arch/powerpc/platforms/85xx/smp.c
> > +++ b/arch/powerpc/platforms/85xx/smp.c
> > @@ -305,10 +310,13 @@ static int smp_85xx_kick_cpu(int nr)
> >             __secondary_hold_acknowledge = -1;
> >     }
> >  #endif
> > -   flush_spin_table(spin_table);
> > -   out_be32(&spin_table->pir, hw_cpu);
> > -   out_be32(&spin_table->addr_l, __pa(__early_start));
> > -   flush_spin_table(spin_table);
> > +
> > +   if (have_spin_table) {
> > +           flush_spin_table(spin_table);
> > +           out_be32(&spin_table->pir, hw_cpu);
> > +           out_be32(&spin_table->addr_l, __pa(__early_start));
> > +           flush_spin_table(spin_table);
> > +   }
> >  
> >     /* Wait a bit for the CPU to ack. */
> >     if (!spin_event_timeout(__secondary_hold_acknowledge == hw_cpu,
> 
> This looks like it's inside an #ifdef CONFIG_PPC32 block, which doesn't make
> sense, so I must be missing a lead-up patch or something? (I looked on the 
> list
> but didn't find anything immediately)

Thanks for catching this.

This is apparently a mismerge due to the code having been previously worked 
on in the context of the SDK tree, which does not have that code inside 
#ifdef CONFIG_PPC32.  When I then applied the result to mainline, everything 
still appeared to work, because there's no real consequence to writing to the 
spin table in this case -- it's just a no-op.  setup_64.c is the part where 
checking booted_from_kexec (or devicetree equivalent) really matters.

-Scott