[PATCH v2 02/16] ARM: b.L: secondary kernel entry code

[Nicolas Pitre]

On Mon, 28 Jan 2013, Will Deacon wrote:

> Hi Nicolas,
> 
> On Thu, Jan 24, 2013 at 06:27:45AM +0000, Nicolas Pitre wrote:
> > CPUs in a big.LITTLE systems have special needs when entering the kernel
> > due to a hotplug event, or when resuming from a deep sleep mode.
> > 
> > This is vectorized so multiple CPUs can enter the kernel in parallel
> > without serialization.
> > 
> > Only the basic structure is introduced here.  This will be extended
> > later.
> > 
> > TODO: MPIDR based indexing should eventually be made runtime adjusted.
> 
> What's your plan for this TODO? Do you aim to merge the code first and add
> that later? If so, maybe add a TODO comment in the code as well?

That should come later as this is probably going to be a non trivial 
task.  We might also decide that the current code is good enough for now 
and it is likely to be the case for a few years.

> > diff --git a/arch/arm/common/bL_entry.c b/arch/arm/common/bL_entry.c
> > new file mode 100644
> > index 0000000000..4e1044612d
> > --- /dev/null
> > +++ b/arch/arm/common/bL_entry.c
> > @@ -0,0 +1,29 @@
> > +/*
> > + * arch/arm/common/bL_entry.c -- big.LITTLE kernel re-entry point
> > + *
> > + * Created by:  Nicolas Pitre, March 2012
> > + * Copyright:   (C) 2012-2013  Linaro Limited
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + */
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/init.h>
> > +
> > +#include <asm/bL_entry.h>
> 
> Similarly with the naming... was there any consensus to replace bL_ with
> something else? I personally find the capitalisation pretty jarring and at
> odds with the rest of the kernel, but "bl" is branch-and-link so that's also
> not much better.

I really find the capitalisation incredibly nice and to the point.  
There is no better way to unambiguously refer to "big.LITTLE" with a 
2-letter prefix.

But as I said, the naming is something I want to change to make this 
code appear more generic as there is nothing really b.L specific here.  
That is a trivial change, once I'm settled on something.

> > diff --git a/arch/arm/include/asm/bL_entry.h b/arch/arm/include/asm/bL_entry.h
> > new file mode 100644
> > index 0000000000..7525614243
> > --- /dev/null
> > +++ b/arch/arm/include/asm/bL_entry.h
> > @@ -0,0 +1,35 @@
> > +/*
> > + * arch/arm/include/asm/bL_entry.h
> > + *
> > + * Created by:  Nicolas Pitre, April 2012
> > + * Copyright:   (C) 2012-2013  Linaro Limited
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + */
> > +
> > +#ifndef BL_ENTRY_H
> > +#define BL_ENTRY_H
> > +
> > +#define BL_MAX_CPUS_PER_CLUSTER	4
> > +#define BL_MAX_CLUSTERS		2
> 
> Again, do you have any ideas/plans on how to remove these constant limits?

Not for the initial merge.  Again, this should serve the systems to come 
in the next few years just fine.  That gives us plenty of time to 
enhance this code with proper dynamic allocation.


Nicolas