From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Fri, 17 May 2013 12:36:22 +0100 Subject: ARM Cortex-A7 support in Linux In-Reply-To: <20130517105500.GE18614@n2100.arm.linux.org.uk> References: <20130517105500.GE18614@n2100.arm.linux.org.uk> Message-ID: <20130517113622.GH23112@mudshark.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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