[PATCH] ARM: Update SMP_ON_UP code to detect A9MPCore with 1 CPU devices

[Will Deacon]

Hi Santosh,

On Tue, Aug 13, 2013 at 02:31:04PM +0100, Santosh Shilimkar wrote:
> On Tuesday 13 August 2013 07:19 AM, Will Deacon wrote:
> > On Mon, Aug 12, 2013 at 07:34:13PM +0100, Santosh Shilimkar wrote:
> >> On Friday 02 August 2013 11:48 AM, Will Deacon wrote:
> >>> I think this an A9-specific register, which reads as 0 on UP A9 and reads as
> >>> some form of PERIPH_BASE for SMP parts. The issue I have is when PERIPH_BASE
> >>> is zero.
> >>>
> >> What do we do here ? Should we document this in the code and proceed ?
> >> Mostly there is no platform with PERIPH_BASE = 0, so its should be fine but
> >> I am open for any other alternative.
> > 
> > The only other alternative I can think of is forcing people to have
> > CONFIG_SMP=n, but that blows away single zImage for your platform.
> > 
> Yep which surely we don't want considering after so much effort we
> have it working first place. How about going ahead with assumption
> that PERIPH_BASE = 0 case doesn't work.

It's been over a month and I can't think of anything better than this
without jeopardising the single zImage effort. However, it also doesn't seem
fair if we rule out the possibility of single zImage for future SoCs which
use 0x0 as their PERIPH_BASE (I don't know of any at the moment).

So how about we go ahead with this, but add a big fat comment to the code in
head.S saying that, if a future SoC *does* use 0x0 as the PERIPH_BASE, then
the check will need to be #ifdef'd or equivalent for the Aegis platform?

Will