ARM Cortex-A7 support in Linux

[Will Deacon]

On Fri, May 17, 2013 at 11:55:00AM +0100, Russell King - ARM Linux wrote:
> On Fri, May 17, 2013 at 12:47:45PM +0200, Marc Zyngier wrote:
> > It depends which feature you're after. Linux supports the GIC
> > virtualization extensions with KVM, for example. But we don't make any use
> > of other things like priorities, split deactivation/priority drop...
> 
> Not that we could make use of priorities anymore as all interrupt handlers
> are now run with IRQs disabled; an IRQ handler can't be interrupted by a
> higher priority IRQ coming in.
> 
> Part of the solution to that is to go back to the original philosophy of
> IRQ handling in Linux - do the least possible amount of work in the IRQ
> and move the heavier stuff off into soft-IRQ context.  Unfortunately,
> many drivers are no longer written like that, and just do a great amount
> of time consuming work in their IRQ handler.

We could also consider using interrupt priorities to have a fake NMI (I
think PPC does this for some cores), which is useful for profiling and
watchdogs, especially now that FIQ is often stolen by the secure world.

I remember dismissing this in the past because I thought it would increase
our GIC distributor accesses, but I don't remember why.

Will