For SMP, Is platform specific secondary startup functionreally needed?

[John Linn]

> -----Original Message-----
> From: Catalin Marinas [mailto:catalin.marinas at arm.com]
> Sent: Wednesday, April 06, 2011 10:36 AM
> To: John Linn
> Cc: linux at arm.linux.org.uk; linux-arm-kernel at lists.infradead.org
> Subject: RE: For SMP, Is platform specific secondary startup
> functionreally needed?
> 
> On Wed, 2011-04-06 at 15:42 +0100, John Linn wrote:
> > > On Wed, 2011-04-06 at 14:48 +0100, John Linn wrote:
> > > > I'm doing some cleanup of SMP patches based on Russell and
> Catalin's
> > > > input which was real helpful. It seems to me that there is not
> always a
> > > > need for a platform specific secondary startup.
> > > >
> > > > I have tested with just letting CPU1 go straight to
> secondary_startup()
> > > > in head.S and it works fine.
> > > >
> > > > I'm probably missing something obvious, if so can you share it?
> > >
> > > We use the pen release mechanism serialise the secondary CPUs
> booting.
> >
> > I'm not saying you can't have it, just that some platforms may not
> need
> > it.
> >
> > Maybe I'm oversimplifying the boot process for our platform, but it
> > seems to be working fine.
> 
> I haven't looked at your code in detail. Does this platform only have
> two cores? If that's the case, you should be fine.

Yes we’re only using 2 cores.  Sounds good as I prefer simple when possible.
I'll put out a new version of patches with this simplified approach.

> 
> But if you have more than one core and you don't serialise the entry to
> secondary_startup(), the __cpu_up() function may get confused.
> 

Understood, more complexity needed for more than 2 cores, makes sense.

Thanks for your time and input,
John

> --
> Catalin
> 
> 


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