Commit 384a290283fde63ba8dc671fca5420111cdac19a seems to break 11MPCore boot

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Wed, Jan 30, 2013 at 11:00:50AM -0500, Nicolas Pitre wrote:
> On Wed, 30 Jan 2013, Punit Agrawal wrote:
> 
> > Hi Nicolas,
> > 
> > I was trying to boot 3.8-rc5 on Realview EB 11MPCore using
> > realview-smp_defconfig as a starting point but the kernel failed to progress
> > past the log below (config attached).
> > 
> > Pawel suggested I try reverting 384a290283fde63ba8dc671fca5420111cdac19a -
> > "ARM: gic: use a private mapping for CPU target interfaces" that you've
> > authored. With this commit reverted the kernel boots.
> > 
> > I am not quite sure why the commit breaks 11MPCore but Pawel (cc'd) might be
> > able to shed light on that.
> 
> That would be appreciated as I don't have any good answer to provide.
> 
> Typically, this patch highlighted problems with bad holding pen 
> implementations where secondary CPUs would enter the kernel all at the 
> same time. In that case the kernel was crashing even before displaying 
> "CPU2: Booted secondary processor".

Well, the patch still looks fine to me.  It might be a good idea to
dump out the value of GIC_DIST_TARGET + 0, just in case there's some
version of the GIC which doesn't advertise its CPU mask via that
register (it should, because it corresponds with SGI0..3, and every
spec I have says that it will be implemented if these IRQs are present).

We do know already that there are some implementations out there which
don't conform to these documents...