Re: [Xen-devel] [PATCH v2 2/6] arm: move GIC SGI kicking into separate function

[Andre Przywara <andre.przywara@xxxxxxxxxx>]

On 12/02/2013 04:01 PM, Ian Campbell wrote:
> On Mon, 2013-12-02 at 12:08 +0100, Andre Przywara wrote:
> > Currently we unconditionally send SGIs to all cores on SMP bringup.
> > PSCI will not need this, so we move this into a function and call it
> > explicitly from the platforms that need it. This gets us get rid of
> > the empty cpu_up() platform functions in ARM32 and the comment in
> > there.
> I don't think this is quite true -- even on a PSCI system the kick is
> required to get past the gate in head.S.
Right, but this is the responsibility of the PSCI handler in the 
firmware, right? I was under the assumption that the semantics of cpu_on 
is to start executing code at the given address, whatever this takes 
internally.
Calxeda firmware for instance does the SGI kick.

> I wonder how this interacts with PSCI implementations which use an SGI
> themselves internally...
>
> > @@ -376,11 +386,6 @@ int __cpu_up(unsigned int cpu)
> >           return rc;
> >       }
> >
> > -    /* We don't know the GIC ID of the CPU until it has woken up, so just 
> > signal
> > -     * everyone and rely on our own smp_up_cpu gate to ensure only the one we
> > -     * want gets through. */
> > -    send_SGI_allbutself(GIC_SGI_EVENT_CHECK);
> > -
> So, I was saying in the 00 mail I'm not sure we can get rid of this
> altogether.
Please note that we do not get rid of this, but just move it. ARM64 
calls it in arm64/smpboot.c, ARM32 non-PSCI platforms call this now 
explicitly by pointing to that function in their platforms/foo.c file.
> But I suppose it is the intention that the platform code always has both
> its own logic and this SGI kick (possibly coalesced) in such
> circumstances? Which is probably ok?
That was my thinking, yes.

Regards,
Andre.


> >       while ( !cpu_online(cpu) )
> >       {
> >           cpu_relax();
> > diff --git a/xen/include/asm-arm/smp.h b/xen/include/asm-arm/smp.h
> > index 1485cc6..a1de03c 100644
> > --- a/xen/include/asm-arm/smp.h
> > +++ b/xen/include/asm-arm/smp.h
> > @@ -21,6 +21,8 @@ extern int arch_smp_init(void);
> >   extern int arch_cpu_init(int cpu, struct dt_device_node *dn);
> >   extern int arch_cpu_up(int cpu);
> >
> > +int cpu_up_send_sgi(int cpu);
> > +
> >   /* Secondary CPU entry point */
> >   extern void init_secondary(void);

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