[PATCH] ARM: smp: Fix Unknown IPI message 0x1

[Russell King - ARM Linux]

On Mon, Jan 17, 2011 at 05:26:35PM +0530, Santosh Shilimkar wrote:
> Commit 'ad3b6993' converted ARM smp_cross_call() to take IPI number
> as a parameter to handle more event than SGI and do_IPI was suppose
> to recover SGI number. But the do_IPI doesn't consider it and it's
> getting detected as 'Unknown IPI message 0x1' with ipi numbers are
> moved to starts from 'IPI_TIMER=2"
> 
> There can be 16 different SGI but only SGI1 is used as IPI so
> only that one is handled in do_IPI as IPI_CPU_START.
> 
> Added IPI_CPU_START because it wasn't used and thought it's
> appropriate. Not sure whether its the right one.

Background:
- we start at 2 because we don't know whether platforms have hard-wired
  SGI1 for startup.
- we don't trap SGI1 at all because we don't use it.
- there's nothing stopping platforms using another SGI to wakeup - we
  don't want to be adding more of this code.

I'd much rather see platforms deciding whether they need to use SGI1
or whether they can switch to SGI0 instead - and we make SGI0 be the
"ignored wakeup" SGI.  If everyone can do that, we get rid of the
silly offset entirely.